I think I have now remembered the moment I became aware of my synesthesia. As a kid I was a bit of an art geek, I liked to read on art history and theory. Reading about Kandinsky there was an introduction that he had some kind of unique way of mapping sounds to colors, followed by a quote from Kandinsky. I was like "This is strange indeed, he got like half of the colors wrong!". Then the book proceeded to explain synesthesia and everything became clear.