This is a simple library to transform a given light wavelength into the corresponding RGB color.
It is based on the different sensitivities to a novel color space called the CIE 193 " XYZ" color space and defined by the CIE colour matching function for 380 - 780 nm in 5 nm intervals :
This allows to simply compute for instance the color of different monochromatic lights:
For more advanced uses, see for instance this blog post computing the color of the sky.