gistfile1.rb

    class BaseColor
      attr_reader :r,:g,:b,:a

      def alpha(v)
        BaseColor.new(r,g,b,v)
      end

      def initialize(r, g, b, a = 1.0)
        @r, @g, @b, @a = normalize(r), normalize(g), normalize(b), normalize(a, 1.0)
      end

      def +(other)
        case other
        when Numeric
          BaseColor.new(@r + other, @g + other, @b + other, @a)
        else
          BaseColor.new(@r + other.r, @g + other.g, @b + other.b, @a)
        end
      end

      def -(other)
        case other
        when Numeric
          BaseColor.new(@r - other, @g - other, @b - other, @a)
        else
          BaseColor.new(@r - other.r, @g - other.g, @b - other.b, @a)
        end
      end

      def to_s
        if a < 1.0
          "rgba(#{r}, #{g}, #{b}, #{a})"
        else
          "#%02x%02x%02x" % [r,g,b]
        end
      end

      def inspect
        if a < 1.0
          "rgba(#{r}, #{g}, #{b}, #{a})"
        else
          "rgb(#{r}, #{g}, #{b})"
        end
      end

      def to_css
        to_s
      end

    protected
      def normalize(v, max = 255, min = 0)
        [[min, v].max, max].min
      end
    end