Why do seahorses change colors? Camouflage is the main line of defense for all seahorses, so it's not unusual for them to not only change colors, but adapt variations in their markings to match and blend into their surroundings.
Here are two good examples of how seahorses can do this. The Lined Seahorse pictured here and the one in the next two photos are of individual Hippocampus erectus seahorses that were received at the same time. Both started out black and were placed in an aquarium together. After this one took to the artificial seaweed-like corkscrew val plant in the aquarium as its hiding place, it turned pale yellowish-green in color. What did the other Lined Seahorse do? See for yourself.
While they are tenatious in their pursuit of food, Seahorses are not aggressive feeders, doing best in a tank with slower moving fish such as the Mandarin Dragonet. Slow swimming Seahorses also do not fare well in aquariums with more than a very light current. The DIY Seahorse Tank which is taller, rather than wider, was specifically designed to house a Seahorse or two and a Mandarin Dragonet.
Thinking about adding a Seahorse to your tank? See the Saltwater Aquarium Fish Compatibility Chart first.