Mermaids are a humanoid species who have adapted to a life underwater.
Freshwater mermaids
Freshwater mermaids usually resemble animals like whales, dolphins, or sharks.
The skin color on their tails usually consist of colors of blue and rarely colors of red and green.
Tropical mermaids
Tropical mermaids are usually very colorful, resembling most tropical fish.
You can find colors like red, orange, yellow, green, dark green, cyan, blue, purple, and even multicolored mermaids.
Arctic mermaids
Arctic mermaids resemble most regular mermaids, with silky white skin, but now with fur on their tails to keep themselves warm.
You can find them usually in colors of white and very light blues.
Subspecies
Lava mermaids
Lava mermaids, or magma mermaids as I have heard some call them, are mermaids that seem to have adapted to very warm environments, warmer than the environments tropical mermaids live in.
They seem to have some kind of scales on their tails, which look like magma. It might be made out of iron or something similar.
Lava mermaids are also immune to fire and lava.