Not exactly.

Again, it depends on where the mermaid is. Lots of sea fans and corals are red, so red hair may be a form of mimicry, which is also a way of avoiding predation. Especially considering the way hair moves, since shark vision cues to movement, outlines, and color differentials, red hair or blue, green, or purple hair would be a boon.

Let me know if you need a link to an ecology textbook.