[SASS] Set of functions to ensure safe colors | https://www.damianwajer.com/blog/scss-functions-to-ensure-safe-colors/

safeColors.scss

// Set of functions to ensure safe colors. 
// Inspired by: 
// - https://pressupinc.com/blog/2014/06/preserving-readability-variable-text-background-colors-sass/
// - http://blog.benjamincharity.com/generate-safe-text-colors-with-sass/

$lightness-bound: 70 !default;
$hue-bound-bottom: 40 !default;
$hue-bound-top: 200 !default;
$brightness-diff-bound: 40% !default;

@function checkColorDangerZone($color, $amount: $brightness-diff-bound) {
  @if ((lightness($color) > $lightness-bound) or (hue($color) > $hue-bound-bottom and hue($color) < $hue-bound-top )) {
    @return darken(desaturate($color, 70), $amount);
  } @else {
    @return lighten(desaturate($color, 50), $amount);
  }
}

@function ensureSafeColor($color, $background-color: null, $amount: $brightness-diff-bound) {
  @if $background-color == null or $background-color == transparent {
    @return $color;
  }

  // Checking text lightness difference from accent background
  $diff: lightness($color) - lightness($background-color);

  // If low brightness difference
  @if abs($diff) < $amount {
    @return checkColorDangerZone($background-color, $amount);
  }

  // High enough contrast; @return original color
  @else {
    @return $color;
  }
}

@function isDarkColor($color: $body-bg, $lightness-bound: 50) {
  @return if(lightness($color) > $lightness-bound, false, true);
}

// Makes a light color darker or a dark color lighter depending on color lightness.
// @param $color [Sass::Script::Value::Color]
// @param $amount [Sass::Script::Value::Number] The amount between `0%` and `100%`
@function distinguishColor($color, $amount) {
  @return if(isDarkColor($color), lighten($color, $amount), darken($color, $amount));
}

// Makes a light color lighter or a dark color darker depending on color lightness.
// @param $color [Sass::Script::Value::Color]
// @param $amount [Sass::Script::Value::Number] The amount between `0%` and `100%`
@function strengthenColor($color, $amount) {
  @return if(isDarkColor($color), darken($color, $amount), lighten($color, $amount));
}