Outstanding collection of about 500 colour-related links on topics comprising Basic Colour Attributes, The Physical Basis of Colour, Colour Vision, Light Mixing Processes, Colorants and Colorant Mixing, Colour Order Systems, Digital Colour Technology, Colour in Art and Design, History of Colour Studies, Colour Education and Further Information.

This is the most complete online discussion of all aspects of colour science. Good explanations and illustrations, and very good discussion of many misconceptions. Not faultless but thought-inspiring. An extremely useful reference at advanced levels. 

The CIE International Lighting Vocabulary, first published in 1938 and revised periodically since then, gives definitions for more than 1400 terms and is by far the most comprehensive and authoritative source on the scientific terminology of light and colour. Although previously very expensive and limited in distribution, it is now freely available online.  

Excellent overview of the colour chemistry and chromatic functions in our natural world.

Overview over philosophical schools/perspectives including the phenomenological one which is of importance for our approach.

Excellent chapter on the history of colour science after Newton.