regenerate (Color::Palette::MonoContrast)

    # File lib/color/palette/monocontrast.rb, line 98
      def regenerate(background, foreground = nil)
        foreground ||= background
        background = background.to_rgb
        foreground = foreground.to_rgb

        @background = {}
        @foreground = {}

        @background[-5] = background.darken_by(10)
        @background[-4] = background.darken_by(25)
        @background[-3] = background.darken_by(50)
        @background[-2] = background.darken_by(75)
        @background[-1] = background.darken_by(85)
        @background[ 0] = background
        @background[+1] = background.lighten_by(85)
        @background[+2] = background.lighten_by(75)
        @background[+3] = background.lighten_by(50)
        @background[+4] = background.lighten_by(25)
        @background[+5] = background.lighten_by(10)

        @foreground[-5] = calculate_foreground(@background[-5], foreground)
        @foreground[-4] = calculate_foreground(@background[-4], foreground)
        @foreground[-3] = calculate_foreground(@background[-3], foreground)
        @foreground[-2] = calculate_foreground(@background[-2], foreground)
        @foreground[-1] = calculate_foreground(@background[-1], foreground)
        @foreground[ 0] = calculate_foreground(@background[ 0], foreground)
        @foreground[+1] = calculate_foreground(@background[+1], foreground)
        @foreground[+2] = calculate_foreground(@background[+2], foreground)
        @foreground[+3] = calculate_foreground(@background[+3], foreground)
        @foreground[+4] = calculate_foreground(@background[+4], foreground)
        @foreground[+5] = calculate_foreground(@background[+5], foreground)
      end