Coral is a colorless marine animal that lives on the ocean floor and can be red, orange and other colors. Any color that appears to be present on coral is a buildup of algae that live on the coral. Like other animals of the sea, coral can change color with emotion.
An individual coral is known as a polyp. Polyps attach themselves to rock along the ocean floor and multiply to form a colony. Each polyp has a hard, protective skeleton at the base that creates a reef when colonies are formed.
Coral are very sensitive to environmental changes such as a change in temperature or pollution. A completely white coral, also referred to as "bleached out," indicates that the animal is stressed. Stressed coral will not allow algae to remain on its surface, placing itself and the rest of the reef it may be attached to in danger.