feature / improving color-yiq function

Created by: wtorsi

Hi, The function is very great (thanks), but it will be much more convenient if we add some arguments, like below. What do you think?

@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;
  }
}