hehe/user/plugins/admin/themes/grav/scss/vendor/bourbon/functions/_color-lightness.scss

// Programatically determines whether a color is light or dark
// Returns a boolean
// More details here http://robots.thoughtbot.com/closer-look-color-lightness

@function is-light($hex-color) {
  $-local-red: red(rgba($hex-color, 1.0));
  $-local-green: green(rgba($hex-color, 1.0));
  $-local-blue: blue(rgba($hex-color, 1.0));

  $-local-lightness: ($-local-red * 0.2126 + $-local-green * 0.7152 + $-local-blue * 0.0722) / 255;

  @return $-local-lightness > .6;
}