PDF::Writer:Color::RGB#to_cmyk
require 'color' p Color::RGB::Red.to_cmyk p Color::RGB::Blue.to_cmyk
で、
#<Color::CMYK:0x40228dd8 @k=0.0, @y=1.0, @m=1.0, @c=0.0> #<Color::CMYK:0x40228860 @k=0.0, @y=0.0, @m=1.0, @c=1.0>
require 'color' p Color::RGB::Red.to_cmyk p Color::RGB::Blue.to_cmyk
で、
#<Color::CMYK:0x40228dd8 @k=0.0, @y=1.0, @m=1.0, @c=0.0> #<Color::CMYK:0x40228860 @k=0.0, @y=0.0, @m=1.0, @c=1.0>