Good idea, but I don't see what color would alert them to danger. People, animals, and anything to do with viscera have color. So, blood is still red. Cows are still white, brown, and black. Humans are still beige. But, plants, soil, the sun, and the sky are all various colors of grey, black, or white. A cave with blood leading into it will still highlight the red.
I guess lava would be grey. Maybe I can do something with that.