PDF::Writer：Color::RGB#adjust_saturation

everyday Ruby 
require 'color'

p Color::RGB::Red.adjust_saturation(10)
p Color::RGB::Green.adjust_saturation(10)
p Color::RGB::Blue.adjust_saturation(10)

p Color::RGB::Red.adjust_saturation(-10)
p Color::RGB::Green.adjust_saturation(-10)
p Color::RGB::Blue.adjust_saturation(-10)

で、

#<Color::RGB:0x40228aa4 @r=1.0, @b=0.0, @g=0.0>
#<Color::RGB:0x402283b0 @r=0.0, @b=0.501960784313725, @g=0.00784313725490185>
#<Color::RGB:0x40227ce4 @r=0.0, @b=1.0, @g=0.0>
#<Color::RGB:0x40227640 @r=0.95, @b=0.0499999999999994, @g=0.05>
#<Color::RGB:0x40226f60 @r=0.0250980392156863, @b=0.476862745098039, @g=0.032156862745098>
#<Color::RGB:0x40226894 @r=0.05, @b=0.95, @g=0.05>