Color Machine Library (CML) is a C library developed for the color industry and color science community which allows you to convert color systems according to standardized formulas.
Using a simple API, transformations can be configured such that even spectral data can be converted easily, accurately and fast.
The library has interfaces for both quick-and-dirty-programming as well as high performance conversion of millions of colors with floating point precision.
CML is published under the Unilicense, or in other words, Public Domain. Usage of CML is free and explicitely allowed.