PDF::Writer：Color::RGB#adjust_hue

everyday Ruby 
require 'color'

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

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

で、

#<Color::RGB:0x40228aa4 @r=1.0, @b=0.0, @g=0.0>
#<Color::RGB:0x402283b0 @r=0.192156862745098, @b=0.501960784313725, @g=0.0>
#<Color::RGB:0x40227d70 @r=0.4, @b=1.0, @g=0.0>
#<Color::RGB:0x40227758 @r=1.0, @b=0.0, @g=0.0>
#<Color::RGB:0x40227078 @r=0.0, @b=0.501960784313725, @g=0.207843137254902>
#<Color::RGB:0x402269ac @r=0.0, @b=1.0, @g=0.4>