I wonder what is this color noise I see when I close my eyes. The visual field is black but there is definitely some subtle color noise which I can "see." I wonder where it comes from.
You are seeing phosphenes.
These have been described in medical notes for thousands of years
They are assumed to be caused by random firing of optic nerves due to stray electrical stimulation in the brain, or pressure on the eye
Other causes are; sudden changes in air pressure, moving from bright light outside into a dark room, violent body motions (like coughing or sneezing), over stimulation (sexual, drugs, grief), diabetic shock, violent sports (boxing, rugby etc); all these may cause pressure on the eye, or over stimulation of the bodies electrical system
If you are getting increased phosphenes, bright flashes of light, or fixed objects appearing with your eyes closed, these may be a sign of eye nerve damage, and a trip to the doctor may be a good idea
Interestingly, this is similar to the CCD device in a camera chip. They are very susceptible to stray electrical charge, and this causes a low level background noise in the picture, even in a totally dark room