Giving mice better color vision
It got me thinking, birds have four color receptors, meaning that they can see in colors we can't even fathom (the article I read this in compared it to having a 3D color map instead of 2D like ours). Could we engineer humans to see color like birds? Or some insects see into the ultraviolet (and some other animals into the infrared), so could we potentially expand our vision into those fields? It's probably unethical, at least right now, but it's a cool possibility.