The reptile species known for changing color based on its mood is the chameleon.

Chameleons are famous for their unique ability to change the color of their skin, which is primarily a result of their emotions, temperature regulation, and communication with other chameleons.
 

The color change is controlled by specialized cells called chromatophores, which contain pigments that can expand or contract to alter the wavelengths of light reflected by the skin.

When a chameleon is calm or content, it may display lighter colors, while darker or more vibrant colors can indicate excitement, stress, or aggression.

This color-changing ability helps chameleons blend into their surroundings and communicate with other members of their species.