Close your eyes and visualize...

I can't see them either. As you say, it's just a memory in your brain and doesn't have anything to do with eyes, if it would, I think it would qualify as hallucination. Same with sounds. I have had audio hallucinations though and they came randomly, not when I wanted to hear them. It can happen especially when you are falling asleep and that's the only time I actually felt like I saw pictures brightly or heard sounds, but always random, not brought up by conscious will.

I see darkness too, at first, but then my imagination kicks in. It's just like watching a movie in my head, and that's cool. When I dream, I'm transported to another place in the confines of my mind. I can replay the dreams, and wonder why. My head is funny because I can do the same thing when my eyes are open.

I think it's really rare .... like 5% of people .

The first time someone told me this - I didn't believe it.

And yes ....I see things, but kind of darker, as in the brightness is lowered .

Yes. I do math and work out angle while building with my eyes close. It takes a certain kind of concentration but I can visualize it and make a plot