I know very little about this, but I watched a program which included a segment about persons who see colors and images that correspond to certain musical notes or chords. Most of these people were highly intelligent, and some had musical genius qualities. You might try searching the internet about this interesting anomaly!
I couldn't tell from your post if you're just curious about this or if you're concerned. Unless these visions interfere with your ability to enjoy music or to complete daily activities, I would consider this ability a gift rather than a condition. I think you have been blessed!
Obviously, if your visions do interfere or bother you, you could go see someone, but you'll probably have to look long and hard to find someone to talk to who has experience in this area.
Good luck!
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Can you see music? 
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