Coral, an organic gemstone, has been protected since the mid 1980s so most “coral” used in new jewellery are varieties of sea plants named after their structure eg. bamboo coral (with its sections/growth similiar to bamboo) and sponge coral (a massive form). These are creamy white in their natural state and are dyed to copy their natural and protected namesake. Bamboo coral is usually dyed red. Sponge coral can be left in its natural creamy white or is commonly died a brick orange/red.
Fossil coral are fossilised ancient corals. It can be dyed although it is usually left its natural beige/neutral tones. The structure of the fossilised coral is clearly seen and adds to the attractiveness of this opaque gem.