YIQ Color Contrast

A naive approach to determing whether a color is "light" or "dark" by checking the lightness value in the HSL color space. It works sometimes, but often produces color pairings that - while technically correct - just look a little "off". The reason for this is that the eye is more sensitive to changes in the orange-blue range than in the purple-green range, so the percieved lightness of a color can change depending its wavelength.

The YIQ color space is designed to take this bias into account. It weighs the different parts of the color according to their impact on our perpection of the color's brightness. By utilizing this color space when doing contrast comparison, the result is a color pairing that appears more natural.

For information on color contrast and the YIQ color space:

• 24 Ways: Calculating Color Contrast
• W3C: Ensure that foreground and background color combinations provide sufficient contrast when viewed by someone having color deficits or when viewed on a black and white screen
• Wikipedia: YIQ

Installation options

NPM

npm install sass-yiq

Bower

bower install sass-yiq

Usage

@import 'yiq-color-contrast'

Configurable Variables

All configuration variables are assigned with the !default flag, so they may be overriden in your project stylesheet.

$yiq-contrasted-dark-default: #000;

The text color to be used when a background is determined to be "light"

$yiq-contrasted-light-default: #fff;

The text color to be used when a background is determined to be "dark"

$yiq-contrasted-threshold: 128;

A a value between 0 and 255. It determines when the lightness of color changes from "dark" to "light".

$yiq-debug: false;

Toggles diagnostic messages.

Functions

yiq-is-light($color, [$threshold])

Returns true if the color is "light" or false if it is "dark".

yiq-contrast-color($color, [$dark], [$light], [$threshold])

Returns the $light color when the $color is dark and the $dark color when the $color is light. The $threshold is a value between 0 and 255 and it determines when the lightness of $color changes from "dark" to "light".

Mixins

@include yiq-contrasted($background-color, [$dark], [$light], [$threshold])

Sets the specified background color and calculates a dark or light contrasted text color. The arguments are passed through to the yiq-contrast-color function.