That's synesthesia.Something I just remembered and didn't think to add earlier is that I can remember being pre-verbal, or still in the learning stages of speaking fluently. Different colours, objects and shapes had their own distinct tones to them; I remember walking in the backyard and hearing the tones change as I looked around. I was quite fond of the sound of blueberry bushes and rhubarb. One of the first things I remember asking myself once I'd attained language was: "What language did I speak before this one?"
I guess I just assumed that I'd learned to translate my innate tonal language into English, which seems like a reasonable assumption for a four/five year old to make.