When I was a kid my dad and I talked about that a lot. There are some perceptual differences between people. For instance I enjoy a visual phenomena called "visual snow". My opthalmologist can't understand what's going on, but in dim lighting or low contrast I see what can best be described as a film grain type texture if you know what I mean. In total darkness I see spots, lines, shimmery and wavy things in different shades of mostly green and purple.