yiq-color.scss

//this function return a color in constrast with the input color
// https://medium.com/@MikeKellyWeb/calculating-color-contrast-with-sass-eff39ef23f96
// Color contrast
// see demo https://codepen.io/fredyang/pen/RwWQJVo
$yiq-text-dark:             $gray-900 !default;
$yiq-text-light:            $white !default;
$yiq-contrasted-threshold:  150 !default
  
@function color-yiq($color, $dark: $yiq-text-dark, $light: $yiq-text-light) {
  $r: red($color);
  $g: green($color);
  $b: blue($color);

  $yiq: (($r * 299) + ($g * 587) + ($b * 114)) / 1000;

  @if ($yiq >= $yiq-contrasted-threshold) {
    @return $dark;
  } @else {
    @return $light;
  }
}