@function yiq-test ($color, $threshold) {
  $r: red($color);
  $g: green($color);
  $b: blue($color);

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

  @return if($yiq >= $threshold, true, false);
}

@function yiq ($base, $dark: $dfr-yiq-color-dark, $light: $dfr-yiq-color-light, $threshold: $dfr-yiq-threshold) {
  @return if(yiq-test($base, $threshold), $dark, $light);
}