SASS mixin that uses modernizr to output fallback color property for browsers that don't support RGBA.

_safe-rgba.scss

/*
 * Outputs a color property with an opaque fallback for browsers that do not support RGBA.
 */
@mixin safe-rgba($property, $color, $fallback-color: opacify($color, 1)) {
  @if opacity($color) == 1 {
    #{$property}: $color;
  } @else {
    #{$property}: $fallback-color;
    .rgba & {
      #{$property}: $color;
    }
  }
}

Glad to help!