Just about every visual illusion possible. Demonstrated beautifully in Phil France's videos to Transitions & Bells. Accompanying higher order auditory musical perfection.
Weird neuro-ophthalmic alterations of the processing mind. With a variety of causes worth looking into.
Cerebral polyopia, photopsia, teichopsia, palinopsia, macropsia, micropsia, telopsia, pelopsia, entomopia, visual snow; cyanopsia, chloropsia, erythropsia.
Seeing red? Does not necessarily stop you from feeling sky blue.