Based on wikipedia, about 4% of the people have synesthesia. However there's only 8 posts that mentioned synesthesia on this entire site, so I am starting this discussion. I think the actual percentage is much higher than 4% and to some extent I believe everyone has synesthesia, if you have strong synesthesia and work as a magician, I think it is important to look at this ability and see it as a gift and utilize it.
Strong synesthesia is usually a gift of birth but could be dismissed or developed later. Personally I did not realize this until I was 15 (because I did not know there was the word “synesthesia” soon after I heard this word I discovered this is how I had been thinking all the time.)
(if the title confuses you, synesthesia refers to when you experience at one thing, it correlates to another thing. For example, when you listen to music, you see colors and shapes and images. A lot of artists have this symptom. Search up "Lsd stimulation" on youtube it gives an interesting presentation.)