I don't know if it's synesthesia but music's always had a colour to me. Major and minor scales in the same key tend to have similar colours just with different tones. A tends to be a bright blue while a minor is more of a darker purply blue. G minor's a dark reddy brown. Dminor is a darker forest green while dmajor is a brighter 'happier' green. C major tends to be a bright yellowy colour, c minor more of a darker yellowy green. B minor takes on a darker yellowy green while b major tends to be an orangy yellow. F and f major start moving into shades of light purple.

It's not just notes though but the octave and tone make a difference too. Distorted instruments like electric guitars or that sound they use in edm music tends to be kind of fuzzy, bass notes are full round and heavy, pianos and bells remind me od looking through the colours through a stained glass window or something.