The stomiidae, which include the viperfish, dragonfish, and loosejaws, are one example of a deep sea animal that evolved to perceive and produce red light because it isn’t naturally present in their environment and most other organisms never hit on that adaptation. In most of this group, tiny red lights can be switched on and off throughout their skin to communicate with their own kind in secret.
More threateningly, some of them have high-powered “floodlights” of pure red just beneath their eyes; almost no other deep sea fish emit actual BEAMS of light to illuminate what they’re looking at because that’d make them a shining beacon to every larger predator in the area, but since it’s red, the only risk ends up coming from their fellow red-light hunters and those remain just uncommon enough to be worth the chance.
In many members of this group, most of all the loosejaws (hence the name), almost the entire skull can naturally detach from the rest of the body on specialized stalks at lightning speed so that their long, hooked jaws can grab prey in an instant, almost the same exact motion as the arm of a preying mantis:
If you were a little fish in this scenario you would see absolutely nothing but darkness around you and possibly feel pretty safe, because maybe you’ve evolved to blend in perfectly with the surrounding void and you can’t see any blue or yellow or green lights coming to get you. You have no idea that there’s been a spotlight right on you all along until its owner’s face flies off to impale you and shove you whole into its giant throat all in less than half of a second :)