I see things in my head all the time, not just when playing music. When I recall stuff, I see it in the form I first saw it in (book page, computer screen, whatever). I do math in my head too, it's like writing on a sheet of glass mentally. 
Music wise, If I've learned something visually (say, off a tab or sheet music) then when I'm playing I can recall the visual and "read" it in my head. The more times I play without looking at the sheet music the fainter the visual gets, but the more rote playing it because (ie. it fades because I don't need it). If I learned something by ear without ever writing it down then my visual becomes the pattern on the fretboard. Course, then I tend to stare at the fretboard if I get lost because that's where my mental visual cue is.
In orchestra I once forgot my music folder at the school where we practiced for a concert. I realized I could see the music in my head and didn't actually need the folder! (it was a christmas concert...how many times have I played sleigh ride?!) The conductor didn't feel that way and luckily the band director of that school was a member so he grabbed my music while he was getting other things. Funny part was I ended up passing my folder to the other pecussionists because my copies were easier to read and ended up playing by memory anyway.
I've been told thats a photographic memory. However, I don't remember names worth a darn (which makes this business a bit tricky....) and unless I concentrate I have trouble remember where I know someone from. Part of that may be from working retail and seeing 50-200 peeps a day. But you'd think a photographic memory would make names easier....*sigh*.
It has its uses outside of music too... I totally tripped out an old 4H leader, I was in college 1200 miles away and she called to ask if I knew where some animal normal temperature info was (this was pre internet, back when you looked everything up in books). I remembered the book title, told her to flip through starting at around page 300, look on the left side of the page for a gray table that takes up 1/2 the page.... it ended up being page 312 or something like that. Funny part is, that was no big deal to me LOL.
As for seeing colors when music plays.....if I try I can. I tend to see more lines and patterns than actual colors, the lines move like you were scrolling through the music side to side. Kinda like waveforms on editing software (which are endlessly fascinating to me!). Colors when you taste something? Now that'd be neat....
Music wise, If I've learned something visually (say, off a tab or sheet music) then when I'm playing I can recall the visual and "read" it in my head. The more times I play without looking at the sheet music the fainter the visual gets, but the more rote playing it because (ie. it fades because I don't need it). If I learned something by ear without ever writing it down then my visual becomes the pattern on the fretboard. Course, then I tend to stare at the fretboard if I get lost because that's where my mental visual cue is.
In orchestra I once forgot my music folder at the school where we practiced for a concert. I realized I could see the music in my head and didn't actually need the folder! (it was a christmas concert...how many times have I played sleigh ride?!) The conductor didn't feel that way and luckily the band director of that school was a member so he grabbed my music while he was getting other things. Funny part was I ended up passing my folder to the other pecussionists because my copies were easier to read and ended up playing by memory anyway.

I've been told thats a photographic memory. However, I don't remember names worth a darn (which makes this business a bit tricky....) and unless I concentrate I have trouble remember where I know someone from. Part of that may be from working retail and seeing 50-200 peeps a day. But you'd think a photographic memory would make names easier....*sigh*.
It has its uses outside of music too... I totally tripped out an old 4H leader, I was in college 1200 miles away and she called to ask if I knew where some animal normal temperature info was (this was pre internet, back when you looked everything up in books). I remembered the book title, told her to flip through starting at around page 300, look on the left side of the page for a gray table that takes up 1/2 the page.... it ended up being page 312 or something like that. Funny part is, that was no big deal to me LOL.
As for seeing colors when music plays.....if I try I can. I tend to see more lines and patterns than actual colors, the lines move like you were scrolling through the music side to side. Kinda like waveforms on editing software (which are endlessly fascinating to me!). Colors when you taste something? Now that'd be neat....