neat, tricking your brain!
As I kid I would press my eyes at night to see the phospene effects. They are caused by changing the pressure in your eyes. Normally light stimulates the retina and the brain interprets this as light. At night there is no light but the pressure stimulates the retina, and your brain interprets this in the ony way it can so you "see" colored lights! Brain hames!
Dont bruise your eyeballs kids.