Synaesthesia is a sense-based neurological phenomenon, not an exercise in imagination; it's not a function of will (that is, I cannot change it - it's automatic).

I've always had it, but didn't know it was a thing until I read Nabokov's "Speak, Memory" when I was 18 decades ago.... I just thought it was a dimension of sense that everyone had and used.

https://en.wikipedia.org/wiki/The_Man_Who_Tasted_Shapes

After reading that years later, I think I finally understood why I could never perceive any high from very high quality MJ/hash that was shared with me when I was a kid, which was fine with me because I really didn't want it (I grew up with stoned elder siblings; I found stoned people very boring. And smelly. I involuntarily had to deal with parental cigarette smoking - ah, the joys of the Greatest Generation that gummint-and-industry ensured got hooked on caffeine, cigarettes and, less widely, alcohol - in that order - to get through the days of Da War.)

I will say this, it's a blessing and a burden. For example, it supports hyper-memory, but it also means I have to process more "incoming", as it were, than is typical; over the decades, it can get tiring unless I find ways to manage/limit the "incoming".