PDF::Writer：Color::CMYK#to_rgb

everyday Ruby 
require 'color'

black = Color::CMYK.new(0, 0, 0, 100)
p black.to_rgb

p Color::CMYK.new(0, 1, 1, 0).to_rgb
p Color::CMYK.new(0, 100, 100, 0).to_rgb
p Color::CMYK.new(0, 100, 100, 0).to_rgb(true)

で、

#<Color::RGB:0x40228b44 @b=0.0, @g=0.0, @r=0.0>
#<Color::RGB:0x40228824 @b=0.99, @g=0.99, @r=1.0>
#<Color::RGB:0x40228518 @b=0.0, @g=0.0, @r=1.0>
#<Color::RGB:0x4022820c @b=0.0, @g=0.0, @r=1.0>