There is some speculation that Richard Feynman had synesthesia as he used to claim that mathematical equations evoked a sense of colour. He couldn't explain it, and he was at least conscious that other people didn't get the same feeling as he did.
That said, I don't think there's any reason to suspect a correlation between synesthesia and genius.
That said, I don't think there's any reason to suspect a correlation between synesthesia and genius.