Ultraviolet.
While we’d love to talk about everyone’s favorite slayer, we’re actually talking about mantis shrimp but since they’re hideous, here’s a photo of Buffy instead. Much better. Here’s the fact – the human eye is ~not~ the most evolved in the world. The mantis shrimp actually is. They are able to see four times as many colors as humans, some of those colors are even ultraviolet.
Ultraviolet.