Interesting. Made me think to write a simple mixin for sass.

    @mixin fg-contrast($bg) {
      background: $bg;
      $textcolor: #ffffff;
      @if lightness($bg) > 50% {
        $textcolor: #000000;
      }
      color: $textcolor;
    }

Could also be done by using the red(), green(), and blue() functions, but lightness was simpler.