This is cool and something I’ve noticed about myself for as long as I can remember. Never knew there was an actual word for my “condition” until I looked it up. Synesthesia, or more specifically grapheme → color synesthesia. Letters and words have always had a color or colors assigned to them in my mind. Makes it easier to remember things sometimes. I also “see” color patterns and shapes when I listen to music, but mostly it’s the letters, numbers, and words.
I have yet to read the entire article on this so I’m not sure what causes it. I credit those little colorful, plastic, magnetic letters and numbers that were always stuck all over our fridge when I was a kid. They must have had quite the effect on me. Thanks Mom and Dad for making my alphabet learning experience so colorful!