Synesthesia is a superpower phenomenon whereby a lucky group of people see color when exposed to stimuli, most commonly sounds. It's the inspiration behind some famous art and music — but it's virtually impossible for mere mortals to get their heads around. This visualization is the best attempt I've yet seen.
Humans evolving into hyper-intelligent beings is a powerful idea in science fiction, but that's probably where the idea will have to stay. Our brains have reached an evolutionary "sweet spot", and we can't get much smarter without making major trade-offs.