chroma.js

chroma.js is a small-ish zero-dependency JavaScript library (13.5kB) for all kinds of color conversions and color scales.

Build Status

Quick-start

Here are a couple of things chroma.js can do for you:

Here's an example for a simple read / manipulate / output chain:

chroma('pink').darken().saturate(2).hex()

Aside from that, chroma.js can also help you generate nice colors using various methods, for instance to be used in color palette for maps or data visualization.

chroma.scale(['#fafa6e', '#2A4858'])
    .mode('lch').colors(6)

chroma.js has a lot more to offer, but that's the gist of it.

Installation

For Node.js: Install the chroma-js npm module using your favorite package manager:

npm install chroma-js
# pnpm add chroma-js
# yarn add chroma-js

Then import the module into your JavaScript:

import chroma from 'chroma-js';

If you just want to use parts of chroma.js and not bundle the entire package, you can import directly from chroma-js/src/* to benefit from treeshaking. For instance, the following import would only result in a 1.24kB bundle increase:

import deltaE from 'chroma-js/src/utils/deltaE.js

And for browsers, download chroma.min.js or use the hosted version on unpkg.com.

You can also just import chroma.js as ES module, as demonstrated in this StackBlitz.

To use chroma.js in Observable notebooks, you can import it like this:

import { chroma } from "@gka/chroma-js"

The interactive documentation continues below (and there's a static version, too) for usage examples. Or use it from SASS using chromatic-sass!

API

chroma

(color)

The first step is to get your color into chroma.js. That's what the generic constructor chroma() does. This function attempts to guess the format of the input color for you. For instance, it will recognize any named color from the W3CX11 specification:

chroma('hotpink')

If there's no matching named color, chroma.js checks for a hexadecimal string. It ignores case, the # sign is optional, and it can recognize the shorter three letter format as well. So, any of these are valid hexadecimal representations: #ff3399, FF3399, #f39, etc.

chroma('#ff3399');
chroma('F39');

In addition to hex strings, hexadecimal numbers (in fact, just any number between 0 and 16777215) will be recognized, too.

chroma(0xff3399)

You also can pass RGB values individually. Each parameter must be within 0..255. You can pass the numbers as individual arguments or as an array.

chroma(0xff, 0x33, 0x99);
chroma(255, 51, 153);
chroma([255, 51, 153]);

You can construct colors from different color spaces by passing the name of color space as the last argument. Here we define the same color in HSL by passing the hue angle (0-360) and percentages for saturation and l*ightness:

chroma(330, 1, 0.6, 'hsl')

New (since 2.0): you can also construct colors by passing an plain JS object with attributes corresponding to a color space supported by chroma.js:

chroma({ h:120, s:1, l:0.75});
chroma({ l:80, c:25, h:200 });
chroma({ c:1, m:0.5, y:0, k:0.2});

chroma.valid

Also new: you can use chroma.valid to try if a color argument can be correctly parsed as color by chroma.js:

chroma.valid('red');
chroma.valid('bread');
chroma.valid('#F0000D');
chroma.valid('#FOOOOD');

chroma.hsl

(hue, saturation, lightness)

Alternatively, every color space has its own constructor function under the chroma namespace. For a list of all supported color spaces, check the appendix.

chroma.hsl(330, 1, 0.6)

chroma.hsv

(hue, saturation, value)

chroma.lab

(Lightness, a, b)

CIE Lab color space. To calculate the lightness value of a color, the CIE Lab color space uses a reference white point. This reference white point defines what is considered to be "white" in the color space. By default chroma.js is using the D65 reference point.

chroma.lab(40, -20, 50);
chroma.lab(50, -20, 50);
chroma.lab(80, -20, 50);

chroma.setLabWhitePoint

(whitePoint)

Sets the current CIE Lab white reference point.

Possible values:
D50 Represents the color temperature of daylight at 5000K.
D55 Represents mid-morning or mid-afternoon daylight at 5500K.
D65 Represents average daylight at 6500K.
A Represents the color temperature of a typical incandescent light bulb at approximately 2856K.
B Represents noon daylight with a color temperature of approximately 4874K.
C Represents average or north sky daylight; it's a theoretical construct, not often used in practical applications.
F2 Represents cool white fluorescent light.
F7 This is a broad-band fluorescent light source with a color temperature of approximately 6500K.
F11 This is a narrow tri-band fluorescent light source with a color temperature of approximately 4000K.
E Represents an equal energy white point, where all wavelengths in the visible spectrum are equally represented. 
chroma('hotpink').lab();
chroma.setLabWhitePoint('F2');
chroma('hotpink').lab();

chroma.getLabWhitePoint

Returns the name of the currently set CIE Lab white reference point. 

chroma.getLabWhitePoint();

chroma.lch

(Lightness, chroma, hue)

The range for lightness and chroma depend on the hue, but go roughly from 0..100-150. The range for hue is 0..360.

chroma.lch(80, 40, 130);
chroma(80, 40, 130, 'lch');

chroma.hcl

(hue, chroma, lightness)

You can use hcl instead of Lch. Lightness and hue channels are switched to be more consistent with HSL.

chroma.hcl(130, 40, 80);
chroma(130, 40, 80, 'hcl');

chroma.oklab

(Lightness, a, b)

Oklab color space

chroma.oklab(0.4,-0.2,0.5);
chroma.oklab(0.5,-0.2,0.5);
chroma.oklab(0.8,-0.2,0.5);

chroma.oklch

(Lightness, chromacity, hue)

chroma.oklch(0.5, 0.2, 240);
chroma(0.8, 0.12, 60, 'oklch');

chroma.cmyk

(cyan, magenta, yellow, black)

Each between 0 and 1.

chroma.cmyk(0.2, 0.8, 0, 0);
chroma(0.2, 0.8, 0, 0, 'cmyk');

chroma.gl

(red, green, blue, [alpha])

GL is a variant of RGB(A), with the only difference that the components are normalized to the range of 0..1.

chroma.gl(0.6, 0, 0.8);
chroma.gl(0.6, 0, 0.8, 0.5);
chroma(0.6, 0, 0.8, 'gl');

chroma.temperature

(K)

Returns a color from the color temperature scale. Based on Neil Bartlett's implementation.

chroma.temperature(2000); // candle light
chroma.temperature(3500); // sunset
chroma.temperature(6500); // daylight

The effective temperature range goes from 0 to about 30000 Kelvin,

f = function(i) {
    return chroma.temperature(i * 30000)
}

chroma.mix

(color1, color2, ratio=0.5, mode='lrgb')

Mixes two colors. The mix ratio is a value between 0 and 1.

chroma.mix('red', 'blue');
chroma.mix('red', 'blue', 0.25);
chroma.mix('red', 'blue', 0.75);

The color mixing produces different results based the color space used for interpolation.

chroma.mix('red', 'blue', 0.5, 'rgb');
chroma.mix('red', 'blue', 0.5, 'hsl');
chroma.mix('red', 'blue', 0.5, 'lab');
chroma.mix('red', 'blue', 0.5, 'lch');
chroma.mix('red', 'blue', 0.5, 'lrgb');

chroma.average

(colors, mode='lrgb', weights=[])

Similar to chroma.mix, but accepts more than two colors. Simple averaging of R,G,B components and the alpha channel.

colors = ['#ddd', 'yellow', 'red', 'teal'];
chroma.average(colors); // lrgb
chroma.average(colors, 'rgb');
chroma.average(colors, 'lab');
chroma.average(colors, 'lch');

Also works with alpha channels.

chroma.average(['red', 'rgba(0,0,0,0.5)']).css();

As of version 2.1 you can also provide an array of weights to
compute a weighted average of colors.

colors = ['#ddd', 'yellow', 'red', 'teal'];
chroma.average(colors, 'lch'); // unweighted
chroma.average(colors, 'lch', [1,1,2,1]);
chroma.average(colors, 'lch', [1.5,0.5,1,2.3]);

chroma.blend

(color1, color2, mode)

Blends two colors using RGB channel-wise blend functions. Valid blend modes are multiply, darken, lighten, screen, overlay, burn, and dodge.

chroma.blend('4CBBFC', 'EEEE22', 'multiply');
chroma.blend('4CBBFC', 'EEEE22', 'darken');
chroma.blend('4CBBFC', 'EEEE22', 'lighten');

chroma.random

()

Creates a random color by generating a random hexadecimal string.

chroma.random();
chroma.random();
chroma.random();

chroma.contrast

(color1, color2)

Computes the WCAG contrast ratio between two colors. A minimum contrast of 4.5:1 is recommended to ensure that text is still readable against a background color.

// contrast smaller than 4.5 = too low
chroma.contrast('pink', 'hotpink');
// contrast greater than 4.5 = high enough
chroma.contrast('pink', 'purple');

chroma.contrastAPCA

(text, background)

New (3.1): Computes the APCA contrast ratio of a text color against its background color. The basic idea is that you check the contrast between the text and background color and then use this lookup table to find the minimum font size you're allowed to use (given the font weight and purpose of the text). 

chroma.contrastAPCA('hotpink', 'pink');
chroma.contrastAPCA('purple', 'pink');

Read more about how to interpret and use this metric at APCA Readability Criterion. Please note that the APCA algorithm is still in beta and may change be subject to changes in the future.

chroma.distance

(color1, color2, mode='lab')

Computes the Euclidean distance between two colors in a given color space (default is Lab).

chroma.distance('#fff', '#ff0', 'rgb');
chroma.distance('#fff', '#f0f', 'rgb');
chroma.distance('#fff', '#ff0');
chroma.distance('#fff', '#f0f');

chroma.deltaE

(color1, color2, Kl=1, Kc=1, Kh=1)

Computes color difference as developed by the International Commission on Illumination (CIE) in 2000. The implementation is based on the formula from Bruce Lindbloom. Resulting values range from 0 (no difference) to 100 (maximum difference), and are a metric for how the human eye percieves color difference. The optional parameters Kl, Kc, and Kh may be used to adjust weightings of lightness, chroma, and hue.

chroma.deltaE('#ededee', '#ededee');
chroma.deltaE('#ededee', '#edeeed');
chroma.deltaE('#ececee', '#eceeec');
chroma.deltaE('#e9e9ee', '#e9eee9');
chroma.deltaE('#e4e4ee', '#e4eee4');
chroma.deltaE('#e0e0ee', '#e0eee0');
chroma.deltaE('#000000', '#ffffff');

chroma.brewer

chroma.brewer is an map of ColorBrewer palettes that are included in chroma.js for convenience. chroma.scale uses the colors to construct. 

chroma.brewer.OrRd

Note that chroma.js only includes the 9-step versions of the palettes (11 steps for the diverging palettes). So, for instance, if you use chroma.js to construct a 5-color palette, they will be different from the "official" 5-color palettes in ColorBrewer (which have lower contrast).

chroma.scale('RdBu').colors(5);
// offical 5-color RdBu:
['#ca0020', '#f4a582', '#f7f7f7', '#92c5de', '#0571b0']

One way to compensate for this would be to "slice off" the extreme colors:

chroma
    .scale(chroma.brewer.RdBu.slice(1,-1))
    .colors(5);

Of course you can also just construct the scale from the official 5-step colors that you can copy and paste from colorbrewer2.org:

chroma.scale(['#ca0020', '#f4a582', '#f7f7f7', '#92c5de', '#0571b0'])

You can access a list of all available palettes via Object.keys(chroma.brewer):

Object.keys(chroma.brewer)
// ['OrRd', 'PuBu', 'BuPu', 'Oranges', 'BuGn', 'YlOrBr', 'YlGn', 'Reds', 'RdPu', 'Greens', 'YlGnBu', 'Purples', 'GnBu', 'Greys', 'YlOrRd', 'PuRd', 'Blues', 'PuBuGn', 'Viridis', 'Spectral', 'RdYlGn', 'RdBu', 'PiYG', 'PRGn', 'RdYlBu', 'BrBG', 'RdGy', 'PuOr', 'Set2', 'Accent', 'Set1', 'Set3', 'Dark2', 'Paired', 'Pastel2', 'Pastel1']

chroma.limits

(data, mode, n)

A helper function that computes class breaks for you, based on data. It supports the modes equidistant (e), quantile (q), logarithmic (l), and k-means (k). Let's take a few numbers as sample data.

var data = [2.0,3.5,3.6,3.8,3.8,4.1,4.3,4.4,
            4.6,4.9,5.2,5.3,5.4,5.7,5.8,5.9,
            6.2,6.5,6.8,7.2,8];

equidistant breaks are computed by dividing the total range of the data into _n_ groups of equal size.

chroma.limits(data, 'e', 4);

In the quantile mode, the input domain is divided by quantile ranges.

chroma.limits(data, 'q', 4);

logarithmic breaks are equidistant breaks but on a logarithmic scale.

chroma.limits(data, 'l', 4);

k-means break is using the 1-dimensional k-means clustering algorithm to find (roughly) _n_ groups of "similar" values. Note that this k-means implementation does not guarantee to find exactly _n_ groups.

chroma.limits(data, 'k', 4);

color

color.alpha

(a)

Get and set the color opacity using color.alpha.

chroma('red').alpha(0.5);
chroma('rgba(255,0,0,0.35)').alpha();

color.darken

(value=1)

Once loaded, chroma.js can change colors. One way we already saw above, you can change the lightness.

chroma('hotpink').darken();
chroma('hotpink').darken(2);
chroma('hotpink').darken(2.6);

color.brighten

(value=1)

Similar to darken, but the opposite direction

chroma('hotpink').brighten();
chroma('hotpink').brighten(2);
chroma('hotpink').brighten(3);

color.saturate

(value=1)

Changes the saturation of a color by manipulating the Lch chromaticity.

chroma('slategray').saturate();
chroma('slategray').saturate(2);
chroma('slategray').saturate(3);

color.desaturate

(value=1)

Similar to saturate, but the opposite direction.

chroma('hotpink').desaturate();
chroma('hotpink').desaturate(2);
chroma('hotpink').desaturate(3);

color.mix

(targetcolor, ratio=0.5, mode='lrgb')

Mix this color with a target color. The mix ratio is a value between 0 and 1. This is the same as chroma.mix but with the first parameter already set. As such, the color space used can be adjusted.

chroma('hotpink').mix('blue');
chroma('hotpink').mix('blue', 0.25);
chroma('hotpink').mix('blue', 0.75, 'lab');

color.shade

(ratio=0.5, mode='lrgb')

Produce a shade of the color. This is syntactic sugar for color.mix with a target color of black.

chroma('hotpink').shade(0.25);
chroma('hotpink').shade(0.5);
chroma('hotpink').shade(0.75);

color.tint

(ratio=0.5, mode='lrgb')

Produce a tint of the color. This is syntactic sugar for color.mix with a target color of white.

chroma('hotpink').tint(0.25);
chroma('hotpink').tint(0.5);
chroma('hotpink').tint(0.75);

color.set

(channel, value)

Changes a single channel and returns the result a new chroma object.

// change hue to 0 deg (=red)
chroma('skyblue').set('hsl.h', 0);
// set chromaticity to 30
chroma('hotpink').set('lch.c', 30);

Relative changes work, too:

// half Lab lightness
chroma('orangered').set('lab.l', '*0.5');
// double Lch saturation
chroma('darkseagreen').set('lch.c', '*2');

color.get

(channel)

Returns a single channel value.

chroma('orangered').get('lab.l');
chroma('orangered').get('hsl.l');
chroma('orangered').get('rgb.g');

color.luminance

([lum, mode='rgb'])

If called without arguments color.luminance returns the relative brightness, according to the WCAG definition. Normalized to 0 for darkest black and 1 for lightest white.

chroma('white').luminance();
chroma('aquamarine').luminance();
chroma('hotpink').luminance();
chroma('darkslateblue').luminance();
chroma('black').luminance();

chroma.js also allows you to adjust the luminance of a color. The source color will be interpolated with black or white until the correct luminance is found.

// set lumincance to 50% for all colors
chroma('white').luminance(0.5);
chroma('aquamarine').luminance(0.5);
chroma('hotpink').luminance(0.5);
chroma('darkslateblue').luminance(0.5);

By default, this interpolation is done in RGB, but you can interpolate in different color spaces by passing them as second argument:

chroma('aquamarine').luminance(0.5); // rgb
chroma('aquamarine').luminance(0.5, 'lab');
chroma('aquamarine').luminance(0.5, 'hsl');

color.hex

(mode='auto|rgb|rgba|argb')

Finally, chroma.js allows you to output colors in various color spaces and formats. Most often you will want to output the color as hexadecimal string.

chroma('orange').hex()

Note that as of version 1.4.0 the default mode is "auto" which means that the hex string will include the alpha channel if it's less than 1. If you don't want the alpha channel to be included you must explicitly set the mode to "rgb" now:

chroma('orange').hex();
chroma('orange').alpha(0.5).hex();
chroma('orange').alpha(0.5).hex('rgb');

You can use .hex('argb') in case you need to encode the color with the alpha channel as first byte rather than the last:

chroma('orange').hex('argb');; // '#ffffa500'

color.name

Returns the named color. Falls back to hexadecimal RGB string, if the color isn't present.

chroma('#ffa500').name();
chroma('#ffa505').name();

color.css

Returns a CSS string representation that can be used as CSS-color definition.

chroma('teal').css();
chroma('teal').alpha(0.5).css();

By default chroma is using the rgb() color space, but you can pass a color space name as first argument. Accepted color spaces are rgb, hsl, lab, lch, oklab, and oklch.

chroma('teal').css('hsl');
chroma('teal').css('lab');
chroma('teal').css('oklch');

color.rgb

(round=true)

Returns an array with the red, green, and blue component, each as number within the range 0..255. Chroma internally stores RGB channels as floats but rounds the numbers before returning them. You can pass false to prevent the rounding.

chroma('orange').rgb();
chroma('orange').darken().rgb();
chroma('orange').darken().rgb(false);

color.rgba

(round=true)

Just like color.rgb but adds the alpha channel to the returned array.

chroma('orange').rgba();
chroma('hsla(20, 100%, 40%, 0.5)').rgba();

color.hsl

Returns an array with the hue, saturation, and lightness component. Hue is the color angle in degree (0..360), saturation and lightness are within 0..1. Note that for hue-less colors (black, white, and grays), the hue component will be NaN.

chroma('orange').hsl();
chroma('white').hsl();

color.hsv

Returns an array with the hue, saturation, and value components. Hue is the color angle in degree (0..360), saturation and value are within 0..1. Note that for hue-less colors (black, white, and grays), the hue component will be NaN.

chroma('orange').hsv();
chroma('white').hsv();

color.hsi

Returns an array with the hue, saturation, and intensity components, each as number between 0 and 255. Note that for hue-less colors (black, white, and grays), the hue component will be NaN.

chroma('orange').hsi();
chroma('white').hsi();

color.lab

Returns an array with the L, a, and b components.

chroma('orange').lab()

color.lch

Returns an array with the Lightness, chroma, and hue components.

chroma('skyblue').lch()

color.hcl

Alias of lch, but with the components in reverse order.

chroma('skyblue').hcl()

color.oklab

Returns an array with the L, a, and b components in the OKLab color space.

chroma('orange').oklab()

color.oklch

Returns an array with the Lightness, chroma, and hue components in the OKLch color space.

chroma('skyblue').oklch()

color.num

Returns the numeric representation of the hexadecimal RGB color.

chroma('#000000').num();
chroma('#0000ff').num();
chroma('#00ff00').num();
chroma('#ff0000').num();

color.temperature

Estimate the temperature in Kelvin of any given color, though this makes the only sense for colors from the temperature gradient above.

chroma('#ff3300').temperature();
chroma('#ff8a13').temperature();
chroma('#ffe3cd').temperature();
chroma('#cbdbff').temperature();
chroma('#b3ccff').temperature();

color.gl

Like RGB, but in the channel range of [0..1] instead of [0..255]

chroma('33cc00').gl();

color.clipped

When converting colors from CIELab color spaces to RGB the color channels get clipped to the range of [0..255]. Colors outside that range may exist in nature but are not displayable on RGB monitors (such as ultraviolet). you can use color.clipped to test if a color has been clipped or not.

[c = chroma.hcl(50, 40, 20), c.clipped()];
[c = chroma.hcl(50, 40, 40), c.clipped()];
[c = chroma.hcl(50, 40, 60), c.clipped()];
[c = chroma.hcl(50, 40, 80), c.clipped()];
[c = chroma.hcl(50, 40, 100), c.clipped()];

As a bonus feature you can access the unclipped RGB components using color._rgb._unclipped.

chroma.hcl(50, 40, 100).rgb();
chroma.hcl(50, 40, 100)._rgb._unclipped;

color scales

chroma.scale

(colors=['white', 'black'])

A color scale, created with chroma.scale, is a function that maps numeric values to a color palette. The default scale has the domain 0..1 and goes from white to black.

f = chroma.scale();
f(0.25);
f(0.5);
f(0.75);

You can pass an array of colors to chroma.scale. Any color that can be read by chroma() will work here, too. If you pass more than two colors, they will be evenly distributed along the gradient.

chroma.scale(['yellow', '008ae5']);
chroma.scale(['yellow', 'red', 'black']);

scale.domain

(domain)

You can change the input domain to match your specific use case.

// default domain is [0,1]
chroma.scale(['yellow', '008ae5']);
// set domain to [0,100]
chroma.scale(['yellow', '008ae5']).domain([0,100]);

You can use the domain to set the exact positions of each color.

// default domain is [0,1]
chroma.scale(['yellow', 'lightgreen', '008ae5'])
    .domain([0,0.25,1]);

scale.mode

(mode)

As with chroma.mix, the result of the color interpolation will depend on the color mode in which the channels are interpolated. The default mode is RGB:

chroma.scale(['yellow', '008ae5']);

This is often fine, but sometimes, two-color RGB gradients goes through kind of grayish colors, and Lab interpolation produces better results:

chroma.scale(['yellow', 'navy']);
chroma.scale(['yellow', 'navy']).mode('lab');

Also note how the RGB interpolation can get very dark around the center. You can achieve better results using linear RGB interpolation:

chroma.scale(['#f00', '#0f0']);
chroma.scale(['#f00', '#0f0']).mode('lrgb');

Other useful interpolation modes could be HSL or Lch, though both tend to produce too saturated / glowing gradients.

chroma.scale(['yellow', 'navy']).mode('lab');
chroma.scale(['yellow', 'navy']).mode('hsl');
chroma.scale(['yellow', 'navy']).mode('lch');

scale.gamma

Gamma-correction can be used to "shift" a scale's center more the the beginning (gamma < 1) or end (gamma > 1), typically used to "even" the lightness gradient. Default is 1.

chroma.scale('YlGn').gamma(0.5);
chroma.scale('YlGn').gamma(1);
chroma.scale('YlGn').gamma(2);

scale.correctLightness

This makes sure the lightness range is spread evenly across a color scale. Especially useful when working with multi-hue color scales, where simple gamma correction can't help you very much.

chroma.scale(['black', 'red', 'yellow', 'white']);

chroma.scale(['black', 'red', 'yellow', 'white'])
    .correctLightness();

scale.cache

(true|false)

By default chroma.scale instances will cache each computed value => color pair. You can turn off the cache by setting

chroma.scale(['yellow', '008ae5']).cache(false);

scale.padding

(pad)

Reduces the color range by cutting of a fraction of the gradient on both sides. If you pass a single number, the same padding will be applied to both ends.

chroma.scale('RdYlBu');
chroma.scale('RdYlBu').padding(0.15);
chroma.scale('RdYlBu').padding(0.3);
chroma.scale('RdYlBu').padding(-0.15);

Alternatively you can specify the padding for each sides individually by passing an array of two numbers.

chroma.scale('OrRd');
chroma.scale('OrRd').padding([0.2, 0]);

scale.colors

(num, format='hex')

You can call scale.colors(n) to quickly grab n equi-distant colors from a color scale. If called with no arguments, scale.colors returns the original array of colors used to create the scale.

chroma.scale('OrRd').colors(5);
chroma.scale(['white', 'black']).colors(12);

If you want to return chroma instances just pass null as format.

scale.classes

(numOrArray)

If you want the scale function to return a distinct set of colors instead of a continuous gradient, you can use scale.classes. If you pass a number the scale will broken into equi-distant classes:

// continuous
chroma.scale('OrRd');
// class breaks
chroma.scale('OrRd').classes(5);
chroma.scale('OrRd').classes(8);

You can also define custom class breaks by passing them as array:

chroma.scale('OrRd').classes([0,0.3,0.55,0.85,1]);

scale.nodata

(color)

When you pass a non-numeric value like null or undefined to a chroma.scale, "#cccccc" is returned as fallback or "no data" color. You can change the no-data color:

chroma.scale('OrRd')(null);
chroma.scale('OrRd')(undefined);
chroma.scale('OrRd').nodata('#eee')(null);

chroma.brewer

chroma.js includes the definitions from ColorBrewer2.org. Read more about these colors in the corresponding paper by Mark Harrower and Cynthia A. Brewer.

chroma.scale('YlGnBu');
chroma.scale('Spectral');

To reverse the colors you could simply reverse the domain:

chroma.scale('Spectral').domain([1,0]);

You can access the colors directly using chroma.brewer.

chroma.brewer.OrRd

chroma.bezier

(colors)

chroma.bezier returns a function that bezier-interpolates between colors in Lab space. The input range of the function is [0..1].

// linear interpolation
chroma.scale(['yellow', 'red', 'black']);
// bezier interpolation
chroma.bezier(['yellow', 'red', 'black']);

You can convert an bezier interpolator into a chroma.scale instance

chroma.bezier(['yellow', 'red', 'black'])
    .scale()
    .colors(5);

cubehelix

chroma.cubehelix

(start=300, rotations=-1.5, hue=1, gamma=1, lightness=[0,1])

Dave Green's cubehelix color scheme!!

// use the default helix...
chroma.cubehelix();
// or customize it
chroma.cubehelix()
    .start(200)
    .rotations(-0.5)
    .gamma(0.8)
    .lightness([0.3, 0.8]);

cubehelix.start

(hue)

start color for hue rotation, default=300

chroma.cubehelix().start(300);
chroma.cubehelix().start(200);

cubehelix.rotations

(num)

number (and direction) of hue rotations (e.g. 1=360°, 1.5=540°`), default=-1.5

chroma.cubehelix().rotations(-1.5);
chroma.cubehelix().rotations(0.5);
chroma.cubehelix().rotations(3);

cubehelix.hue

(numOrRange)

hue controls how saturated the colour of all hues are. either single value or range, default=1

chroma.cubehelix();
chroma.cubehelix().hue(0.5);
chroma.cubehelix().hue([1,0]);

cubehelix.gamma

(factor)

gamma factor can be used to emphasise low or high intensity values, default=1

chroma.cubehelix().gamma(1);
chroma.cubehelix().gamma(0.5);

cubehelix.lightness

(range)

lightness range: default: [0,1] (black -> white)

chroma.cubehelix().lightness([0,1]);
chroma.cubehelix().lightness([1,0]);
chroma.cubehelix().lightness([0.3,0.7]);

cubehelix.scale

You can call cubehelix.scale() to use the cube-helix through the chroma.scale interface.

chroma.cubehelix()
    .start(200)
    .rotations(-0.35)
    .gamma(0.7)
    .lightness([0.3, 0.8])
  .scale() // convert to chroma.scale
    .correctLightness()
    .colors(5);

Changelog

3.1.2

3.1.1

3.1.0

3.0.0

2.6.0

2.5.0

2.4.0

2.3.0

2.2.0

2.0.3

2.0.2

2.0.1

2.0.0

1.4.1

1.4.0

1.3.5

1.3.4

1.3.3

1.2.2

1.2.0

1.1.0

1.0.2

1.0.1

1.0.0