Factors that influence ethnic variations in merfolk

Merfolk physiological traits and to a lesser extant personality dispositions are partially determined by elemental forces, much as elemental ethnicity affects humanoids in Scarterra.   The main difference is that Merfolk, like other Scaraquans, are constantly exposed to the elemental energy of Water, so they physically resemble humans or elves with a high degree of "watery" traits as outlined below.  But Scaraquans are not creatures of water alone.  

Baseline Merfolk Cosmetic Traits

  Most merfolk have light blue, light green, or silvery skin or some combination of these colors.   Most merfolk have dark blue, dark green, or black hair.   A plurality of merfolk have green eyes. blue, grey, and brown eyes are uncommon but by no means unheard of.   Most merfolk have relatively small noses and fairly lithe and curvy bodies.   Most merfolk tend to be emotional and empathetic. They also tend to be indirect in their social dealings.    

icy merfolk traits

  Merfolk live mostly in cold waters to develop "icy" traits mixed in with their default "watery" traits. Not many merfolk live in cold waters.   Icy merfolk have secondary traits that Scarterrans would call "airy". They often have a pale white wash over their base colors, have curlier hair, larger nostrils, and are a bit lankier than average merfolk.   Eyes are commonly grey with blue as the second most common color. Brown, gold, and silver eyes are rare but not unheard of.   They are likely to be more stoic and emotionally closed off than the average merfolk.    

rocky merfolk traits

  Merfolk that live mostly near the ocean floor tend to develop "solid" or "rocky" traits mixed in with their default "watery" traits. Scarterran scholars would call this "earthy." As earthy as someone can be surrounded by water. This is fairly common for Merfolk since they prefer to live near the ocean floor.   Rocky merfolk are a bit stockier than average merfolk. They have the same common hair and skin colors than most merfolk but the hues are a shade darker. They often but my no means always have what we would call "Roman noses."   Eyes are usually black or dark green. Brown, blue, grey, or metallic eyes are rare but not unheard of.   Rocky merfolk tend to be more pragmatic and straight forward than the average merfolk.    

sky fire touched merfolk

  Merfolk from warmer shallower waters are often considered to be touched by the sky's fire and manifest what Scarterrans consider fiery traits.   Hair tends to be even messier than normal for merfolk (though it's hard to tell because their hair is usually buffeted by water). You might occasionally see a few redheads like Arial from The Little Mermaid but usually watery hair traits are fighting with fiery hair traits resulting in various shades of purple hair or black hair with a slightly red tint, or less commonly brown hair.   Merfolk that are fire touched tend to be creative and wear their emotions on their sleeves.    

Differences between deep and shallow merfolk

  Merfolk that live towards the surface of the sea tend to be very anthromorphic resembling Scarterran humans or elves with fishtails, as similar to humans as The Little Mermaid or Splash but Merfolk that hail from deeper waters tend to be more icthyomorphic having more pronounced fish traits such as visible gills or fin-like ears, spiny hair or beards, non-human like eyes.   Merfolk tend to be a beautiful people, even the icthyomorphic merfolk tend to have an alien beauty.   Because most of the merfolk that Scarterrans see are nearly always merfolk that live near the surface, most merfolk that Scarterrans glimpse are very anthromorphic. Most land folk are completely unaware that more icthyomorphic merfolk exist.    

How does this all apply?

  Most merfolk have multiple influences on their ethnicity and appearance. For obvious reasons, most merfolk display at least some watery ethnic traits.   Merfolk that live in moderate depths in temperate waters away a moderate distance from both the surface and the ocean floor are probably only going to manifest cosmetic watery traits and have little to no noticeable traits of the other three elements. They are probably going to be mostly anthromorphic with one or two exotic touches apart from their fish tail.   A merfolk that lives in cold and shallow waters is likely to have watery, icy, and rocky traits while be highly anthromorphic.   A merfolk that lives in warm, deep waters near the ocean floor is likely to have watery, fiery, and rocky traits and be highly and have pronounced icthyomorphic traits.   There are rare places in Scaraqua where geothermal vents create warm waters far from the surface. "Magma Merfolk" born near these places will embody mixed traits manifest fiery and rocky traits with much less water influence than you would normally see on a merfolk.