"To put the matter in Aristotelian terminology, visual impressions are prior in the order of being to concepts pertaining to physical color, whereas the latter are prior in the order of knowing to concepts pertaining to visual impressions."

Next Quote

Having visual impressions is, of course, necessary for seeing things, but it is not sufficient. What must be added is not anything sensible. And it is precisely this that unlocks the outer world for us; for without this non-sensible something, each of us would remain locked up in his inner world.

— Gottlob Frege