I've been trying for years to visualize. My SO is an artist and my mother a psychologist, so I've been trying to gets tips and tricks from them. I never managed to even get a hint of color.
While I was in jail I managed to imagine images in vivid color and detail several times, but never on demand. It would happen randomly when I was just lying, bored, thinking about stuff. Each time was one of the most amazing experiences of my life. It was like going from being a caveman looking at scratchings on a wall, to straight into a 3D IMAX movie. The quality was that spectacular, with bright colors and completely 3-dimensional. Since I left jail it hasn't happened again a single time.
I have to wonder if that's how others see inside their minds? If so, I am in awe.
Anyway this might just be specific to me but something to think about.