Why do I see rainbow dots?

These perceptions are what scientists call “phosphenes” — the sensation of light that’s not actually caused by light. They can start in the eye or the brain, but the ones you are talking about are usually due to the normal functioning of the retina.

Why do I see little dots everywhere?

Most eye floaters are caused by age-related changes that occur as the jelly-like substance (vitreous) inside your eyes becomes more liquid. Microscopic fibers within the vitreous tend to clump and can cast tiny shadows on your retina. The shadows you see are called floaters.