# File lib/sass/script/functions.rb, line 265
    def rgba(*args)
      case args.size
      when 2
        color, alpha = args

        assert_type color, :Color
        assert_type alpha, :Number

        unless (0..1).include?(alpha.value)
          raise ArgumentError.new("Alpha channel #{alpha.value} must be between 0 and 1 inclusive")
        end

        color.with(:alpha => alpha.value)
      when 4
        red, green, blue, alpha = args
        rgba(rgb(red, green, blue), alpha)
      else
        raise ArgumentError.new("wrong number of arguments (#{args.size} for 4)")
      end
    end