# File lib/sass/script/functions.rb, line 693
    def saturate(color, amount = nil)
      # Support the filter effects definition of saturate.
      # https://dvcs.w3.org/hg/FXTF/raw-file/tip/filters/index.html
      return Sass::Script::String.new("saturate(#{color})") if amount.nil?
      _adjust(color, amount, :saturation, 0..100, :+, "%")
    end