I have synesthesia and am not on the spectrum, I had no idea that seeing letters in color or numbers spatially or associating tastes with sounds etc was unusual until I read an article about it in Time magazine about a decade ago. I've asked virtually everyone in my family about it (20 cousins, my kids, siblings etc) and I seem to be the only one. If I hadn't read the article, I wouldn't know!
That said, I am very much a visual learner and worker and a very fast reader. In retrospect, I think it's because seeing and learning are so closely intertwined for me. I can read something and know it, I can see something and learn it. However, I sometimes struggle when new tasks are explained or I'm given only verbal instructions - like over the phone.