Well, red in nature doesn't always need to mean blood. It can also be a signal to other animals, even if they don't have red blood. Red is pretty hard to camo

Well, red in nature doesn't always need to mean blood. It can also be a signal to other animals, even if they don't have red blood. Red is pretty hard to camouflage in nature, and it really stands out. Sometimes it's for attracting, such as red apples, fruit/berries, or flowers. By attracting other animals, it helps the signaler. Sometimes it's to signal danger, as in red poisonous mushrooms, or animals that have red bodies and are toxic or don't taste good. ("don't eat me") I guess what I'm saying is that red was a signal long before humans came on the scene, and I think we are still on the look out for it because of those same evolutionary clues.