A journey through some visual illusions show how a simple physical concept of human colour vision doesn’t work. It’s all about perception, not physics.
lightness
“A human observer is able to recognise the colour of objects irrespective of the light used to illuminate the objects.” “Colour constancy does not exist in humans.” Which is right?
Lightness is key to the depiction of materials, textures, edges, and form. Illusions can confound the viewer, and it is vital to map the lightness of your motif to that of your painting.
What do we actually perceive of colour?
The Eclectic Light Company 