I had an idea where some female mermaids have fins that change to the color of lipstick they are wearing. So we have Bri, who’s wearing the great top, she’s wearing a gold lipstick so her fin is gold. We have Mel, who’s trans, and paints her fin to either match or not match her lipstick. Then there is Jay who is capable of changing their fin color but most times chooses not to. Their fin wasn’t fully developed at birth so they found a lost rubber swimming fin humans use and attached it with clams.
Mermaids have yellow eyes to aid them in seeing in the dark.