Tropical warm water fish are often very colorful. Since they have so much color to attract mates it also makes them venerable to predators.
They often have a "fake eye" pattern on their bodies to confuse larger fish. The fake eyes can be elaborate and include under eye dark circles. The larger fish see these fake eye patterns and aim for the wrong part of the fish to grab. This often gives the smaller fish the chance to get away from the predator.