I have known many blind children, some who were blind from birth. And they have absolutely no idea what anything looks like! They can't even imagine seeing. I can perhaps imagine what it might be like to be blind because I can cover my eyes and not be able to see. Blind from birth people have no experience to be able to imagine sight.
They dream of course, but in words, sounds and feelings.
NIghtmares too.
I am fully sighted and often wake after a dream, only to remember the feelings I dreamt, not what I saw.