rationalskepticism.org

romansh wrote:

DavidMcC wrote:
I wouldn't call it an illusion myself, because it isn't really misleading you, rather,

I know it is a mixture of three relatively monochromatic colours none of which are yellow.

If you don't call it an illusion, fine.

Perhaps you missed the bit where I explained why seeing yellow without any monochromatic yellow being present is not a true illusion, unless you think that seeing almost any non-monochromatic colour, that involves significant excitation of more than one cone type is an "illusion". Rather, it isthe visual system limitting the number of different perceived colours, probably to limit the size of the visual cortex. If yellow is defined as any wavelength spectrum that leads to approximately equal firing rates of MW and LW cone cells, then seeing yellow without any photons that are at or near the monochromatic yellow wavelength is not an illusion, rather, it is just space-saving in the VC. If you see yellow under different conditions than this, THEN it is a colour optical illusion.