Efros is a Federation member world.
The Planet is a class M planet under "Snowball" conditions, completely frozen over.
The Inhabitants are long lived humanoidds who are spiritual. Their respect for their delicate pockets of ecology on Efros has led them to develop biological and medical sciences farther than any other.
Generally Efrosians are blue people with white hair. They have the full ranges of sizes and physical qualities of humans. The main physical difference is in terms of temperature tolerance. Efrosians are much better adapted to cold, but less well able to tolerate great heat.
Efrosians and Andorians appreciate similar climates.
There is a difference in coloring between Efrosian Males and Females.
Males are dark blue with light blue "racing stripes' down each side of the head and body.
Females are light blue with dark bluw racing stripes.
The thickness of these stripes varies from individual to individual. The patterns of the stripes across the face vary, a little, making individuals distinctive once one has learned to watch for this.
Lips and mucus mebranes are light blue. Efrosians have striking electric blue eyes.
Very rarely, Efrosians are born with reverse coloring. That is, Males can be born light blue with dark blue racing stripes, and females can be born dark blue with light blue "racing stripes."
Efrosian science has long since established that such people are just that - color-revered, and suffer no other ill effects. However Efrosian Culture is uncomfortable with such people. They suffer from social stigma and stereotypes of reversed gender behavior. Reversed color males are expected to be effeminate, dainty and delicate. Reverse colored Efrosian females are expected to be "butch" and overly aggressive.
Such people often battle such expectations and stereotypes all their lives.
Many such people escape Efros and find that the outer Galaxy cannot tell proper Efrosian coloring from a pickle.
Efrosians appear in the documentation of the Movie "Star Trek IV: The Voyage Home" where at least two characters are described as "Efrosian".
The Efrosian race was detailed in Fasa's Star Trek IV Source book Update- a Game manual for FASA's Star Trek the Role Playing Game.
Colors or Ridges?Edit
Now. Is this guy Efrosian (B&W Photo on the left)?
Or is this guy (Color Photo on the Right)?
Canon is unclear, however production documents run a close second to canon and they indicate that both men are Efrosian.
Your mileage may vary.
I know mine does, as described below.
In ST-OM the left hand picture depicts an Efrosian.
The right hand picture depicts a Golden Orion.
This is at variance with what fannon and canon say. Sue me. But I like the STIV Helmsman and Kurtwood Smith as the Federation President in STVI as Golden Orions.