Sometimes I see purplish swirls of color in the darkeness. I'm not sure what this is, but I know that when you are in darkness your eyes produce some kind of "visual purple" compound that helps you see in the dark.
Found an article about this stuff : http://en.wikipedia.org/wiki/Rhodopsin



The little pixels that we see while looking at the sky are shadows of dead cells and other garbage that is suspended in the liquid inside our eyes. This liquid can move and has some inertia. So when we look at the sky and move our eyes the liquid moves slower than the rest of the eye itself. So we see these pixels slowly following our eye movements.