Blue "Magic Warrior, Water Demon"

About

Blue is traveling with Keel and Ravi while looking for revenge against Kurokiri Setsuna.

While in his human form he has black hair, dark colored eyes, and rounded ears.
When he transforms into his monster form his hair becomes lighter until it is grey. His ears become pinted and his eyes turn light blue. The biggest change are the markings he has on his face, over his cheeks, nose, and forehead.

Source: Wikipedia