There is a disease called black spot disease which his caused by parasitic fluke larvae. It looks like it might be the start of that. This disease causes black pigment like in the photo, very similar. Sometimes it can be difficult to distinguish it from regular black pigmentation. Some fish change color as they grow. If the markings seem even and regular this could be the case but if they grow, spread, or are uneven on each side of the fish it may be the disease.
Generally the fish is okay and the parasite doesn't do much to them. The exception is if the infection gets too close to the eye it could cause blindness.