If they were small and in full color; they may have been fed melanocyte stimulating hormone. You can bring out the colors in older fish with carotene, astaxanthin and an other one for yellow, in their food.
Recently I saw imported Malaysian red turquoise and heckel cross with very bright colors. Is there any way one can say artificial coloring feed were given by observing the fish.
If they were small and in full color; they may have been fed melanocyte stimulating hormone. You can bring out the colors in older fish with carotene, astaxanthin and an other one for yellow, in their food.