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.
On visual snow - here's my hypothesis for you to test.
It has been wondered to be a form of migraine or cortical hyper-excitability.
I, as suggested by a few others, think it is probably 'physiological noise' in the system – akin to tinnitus – and the more you look for it the more you might see it.
I propose it might therefore be completely normal.
I'm pretty sure I can see the effect myself if I look hard for it, especially on plain walls, even a computer screen.
I was up one night to the bathroom – half asleep, I could see it distinctly even more.
It’s rather like what you see when you close your eyes in the dark.....Eigengrau.
Best policy is self-reassure and to ignore: concentrate only on what you are looking at.
Same as tinnitus – don’t think about it and awareness of it just seems to fade away….
And just make sure of one more thing: