It is freely available under the BSD-3-Clause terms.
Colour is an affiliated project of NumFOCUS, a 501(c)(3) nonprofit in the United States.
Colour features a rich dataset and collection of objects, please see the features page for more information.
The How-To guide for Colour shows various techniques to solve specific problems and highlights some interesting use cases.
The main technical reference for Colour and its API is the API Reference.