Vitamin D basically IS presence of/lack of colour - because it is only produced when certain wavelengths of light ('colours') are present. As well as vitamin D there are also many other chemicals in the body which need certain wavelengths of light to be produced. See for instance web.mit.edu/dick/www/pdf/286.pdf (an 1980s but reasonable article not written by quacks)
That's an interesting thought and cheers for the link. I guess I tend to think of colours as only within the visual spectrum, and my understanding was that the chemical reactions were from UV and above, but I can see now that's kind of arbitrary thinking.
