Colours, including brown (most common in Western Guadeloupe), green and sometimes grey - depend on zooxanthellae types which, depending on content of particular proteins, can even cause red fluorecence as seen in title photograph - in total absence of special fluo lights.

Zooxanthellae are microscopic photosynthetic algae that live in symbiosis with corals. The latter provide shelter in exchange of which the zooxanthellae supply certain nutriments (including glucose and aminoacids relutling from photosynthesis) that enable them to eventually produce the calcium carbonate used to form their structure.