Iridescence
The neon tetra has a light-blue back over a silver-white abdomen. During the night, the blue and red become gray or black as the fish rests. It reactivates once it becomes active in the morning. This peculiar change is due to the neon tetras capacity to change the color of its iridescent stripe in response to lighting conditions. This change is produced by guanine crystals in their cells that reflect light.
