Changing colours

This are Long-nosed Emperor - Lethrinus olivaceus, they have the ability to change their colours as they swim between the water column and the reef, probably to make them less visible to their prey or even predators.
In the picture, the fish on the left is swimming towards the reef, hence it takes on the markings on the body. The fist on the right is even-coloured of silverish as it moves to the water column.