Didn't I already do this? Nope apparently not. Because in the empire request for the Zarethians I had the main race listed as human, so... yeah.
I appearance the Zarethians are normally fair skinned with a variety of hair and eye colors. These can be as normal as black hair, to as abnormal as anime style blue and green hair. The lighter the color of the hair, the rarer that hair is, just like with human hair colors, like blond and black. Same with the eyes. Normally the Zarethians are Caucasian in appearance, but there are rarer cases of Oriental or other racial types found on Earth appearing as well.
They have a very high affinity with magic, but they use 'chi' sort of, instead of using an organ they naturally have magic flowing through them. Most Zarethians either don't have any magic in them or aren't very strong with it. But those who are somewhat strong with it are sent to the priesthood to home their magical abilities, leading to some incredibly strong spellcasters. After they are fully trained with magic, they normally become battle mages for the Navy, or Zarethian marines. They don't use words, so much as thoughts and concentration to manipulate magic. The Zarethians can naturally live for up to a thousand years, but due to war, sickness, or injuries of the flesh, they leave their bodies sooner than they would naturally.
The Zarethians are very intelligent as a people and are generally selfless, because in many situations selfishness can lead t the deaths of many, many people.