color-tools is a Ruby library to provide RGB, CMYK, and other
colourspace support to applications that require it. It also provides
152 named RGB colours. It offers 152 named RGB colours (184 with
spelling variations) that are commonly supported and used in HTML,
SVG, and X11 applications. A technique for generating a monochromatic
contrasting palette is also included.

Homepage:
http://rubyforge.org/projects/ruby-pdf
