I believe you, It think I'm also the same; however for me at least, I feel like I can "think" of what something looks like. This is hard to explain since its very "personal" way its easier to say "i can see a square" nope I can't see anything but I can "think" of a square.

The whole imagine a ball in your mind. Now tell me what colour it is. No idea you tell me :D I can pretend and make up a color or go with what my gut tells me which is the most common color my brain was probably trained on.(red). but in reality I don't see any ball.