Do you see colors when you close your eyes?

I think this is more of a physiology than a philosophy question. When you deny yourself the use of any of your senses, the mind will often just make stuff up to "fill in the silence". If you put someone in a tank of water where they are floating freely in complete pitch darkness and as absolute silence as possible, sooner or later the mind starts to invent things - you start to hear, feel, see and even smell things which are simply not there because the mind need input in order to function properly. So, when you close your eyes, the mind starts this process with simple colors and then progresses to images. Some people can manipulate what they see, by controlling their minds: nothing mystical need be invoked in this matter: it's pretty straight-forward, logical and can be demonstrated rather easily.