Full Idea
The origin of all colours in bodies is plainly deduced out of the various degrees of rarity and density, variously mixed and compounded.
Gist of Idea
Colours arise from the rarity, density and mixture of matter
Source
Kenelm Digby (Two treatises [1644], I.29.4), quoted by Robert Pasnau - Metaphysical Themes 1274-1671 22.5
Book Reference
Pasnau,Robert: 'Metaphysical Themes 1274-1671' [OUP 2011], p.506
A Reaction
We are still struggling with this question, though I think the picture is gradually become clear, once you get the hang of the brain. Easy! See Idea 17396.
Related Ideas
Idea 16726 Why can't we deduce secondary qualities from primary ones, if they cause them? [Buridan]
Idea 17396 The colour of gold is best explained by relativistic effects due to fast-moving inner-shell electrons [Scerri]