Color Fallbacks

_color-fallback.scss

// Mixin that uses the format-color function to create a color fallback for a property

@mixin color-fallback($property, $hsla-color) {
  #{$property}: format-color($hsla-color, hex);
  #{$property}: format-color($hsla-color, rgb);
  #{$property}: format-color($hsla-color, rgba);
  #{$property}: format-color($hsla-color, hsl);
  #{$property}: format-color($hsla-color, hsla);
}

example.scss

@import "color-fallback";

body {
  @include color-fallback(color, hsla(0, 0%, 15%, 1));
}

format_color_function.rb

# Custom Sass function

module Sass::Script::Functions
  def format_color(color, format)
    assert_type color, :Color
    assert_type format, :String
    result = case format.value
    when 'hsla'
      "hsla(%d, %d%%, %d%%, %f)" % (color.hsl + [color.alpha])
    when 'hsl'
      "hsl(%d, %d%%, %d%%)" % color.hsl
    when 'rgba'
      "rgba(%d, %d, %d, %f)" % (color.rgb + [color.alpha])
    when 'rgb'
      "rgb(%d, %d, %d)" % color.rgb
    when 'hex' # really just rgb
      "#%s" % color.rgb.map { |c| c.to_s(16) }.join('')
    end
    Sass::Script::String.new(result)
  end
  declare :format_color, :args => [:string]
end

result.css

body {
  color: #262626;
  color: rgb(38, 38, 38);
  color: rgba(38, 38, 38, 1.000000);
  color: hsl(0, 0%, 15%);
  color: hsla(0, 0%, 15%, 1.000000); }

Tested with:

% sass -r ./format_color_function.rb example.scss > result.css