It's not uncommon for cichlids to change colors depending on their stress level, mating rituals, etc. It's also not uncommon for cichlids to change colors between the fry stage and adulthood, sometimes significantly. In fact, it's not uncommon for young fry to bear little resemblance to their parents, which often makes it difficult to quickly determine the species of fry in a cichlid community tank that contains multiple species of breeding pairs.
For Telmatochromis sp. "temporalis shell," the above is very true. Past blog posts (here and here) focused on this fun little cichlid and its fry. Beginning a very white, almost translucent, often with light black stripes, this fish will turn brilliant smoky black at about the three month mark. And the change will occur nearly overnight.
Recently, one of the surviving temporalis juveniles in my 75g community cichlid tank had started swimming out in the open. About 3/4" long and almost solid white in color (top photo), it was too large to be consumed by even the largest of the other cichlids in the tank. Just the other day, I no longer spotted it. Usually, it appeared mostly during feeding time. Then suddenly, I didn't see it for a few days. I thought it might have died. Turns out my eye had been trained to look for a small white cichlid when I should have been looking for a small black one. In a matter of a few short days, the transformation was complete. The bottom photo above shows the same juvenile, now at about 1".
The Cichlid Room Companion
Tropical Fish Hobbyist
American Cichlid Assoc.
African Cichlid Hub