And who says it has to be a seahorse? Shimmer Seahorse Fin Headband Costume This magical aquatic accessory will work for anyone, adult or child, who is looking for the final piece of their costume. too! The headband itself is a sea green, while the spines on the fins are a bright magenta.Scales flash and shine in the sun's rays, coral pops from the gray sea floor in pinks and yellows, and the plant life also features bursts of color and texture.