From Holocron - Star Wars Combine
|Average Height||1.8 meters |
|Skin color||Pale to dark brown, red, orange and yellow |
|Distinctions||Horns, facial tattoos |
|Known Members||List of known Zabraks|
Biology and appearance
This near-human species had several sub-species, each of which was distinguishable by the vestigial horns which ringed their heads. They are known for their ability to withstand great amounts of pain. The Zabrak races were native to the planet Iridonia, although were one of the first to introduce interstellar travel, and thus are widely spread around the galaxy.
These horns grew at puberty in varying patterns and signified that the time of their rite of passage was drawing near. 
The horns were one trait shared by the many Zabrak subspecies, which were divided by a number of physical characteristics that differed from subspecies to subspecies. These could include different skin tones (which included peachy white, pure white, yellow, red, tan, brown and black), horn patterns, hair growth (though it should be noted that Zabraks, unlike Humans, could not grow eyelashes or facial hair – there were some exceptions, who had eyebrows) and eye color (which have certain pigmentations that Humans lack, such as purple, yellow, red, and orange). 
Another of the traits that made Zabrak instantly recognizable were their facial tattoos, which were made up of thin lines received during their rite of passage. These could symbolize many things, including but not limited to family lineage, place of birth, or even a design that reflected their individual personalities. 
Zabraks were capable of breeding with Humans, and a hybrid sub-species evolved on Dathomir called the Dathomirians, formed from the mating of Nightbrother Zabraks and Nightsister Humans. 
Culture and personality
Considered something of a headstrong species, they are independent and capable - yet prone to biting off more than they can chew. A hardy species that can take a great deal of stress, both inner and outer, xenobiologists have varyingly tried to tie this trait to different strands in the Zabrak genetic makeup, but it seems every few years another one comes along that disproves the one before it.
Their culture is nominally broken into eight major colonies, and each Zabrak is said by Iridonian law to belong to one of them. However this is often muddied by the interbreeding brought about by their great travels across the galaxy, and today it is not uncommon to find a Zabrak who claims membership in as many as five of the different colonies.
Zabrak were often seen by most other species as being single-minded, an observation that was not terribly incorrect. This single-minded determination came from the fact that they were a race with a strong sense of self-assuredness, confident that they were able to accomplish any task that they set out to do. However, this did not lead a Zabrak to develop a sense of prideful superiority towards others, though there was often the occasional competition between colonies. This was not seen as a negative, however, for the Zabraks believed that the various experiences of the different colonies only served to add values to the race's overall value to the galaxy. 
Zabrak from Iridonia were considered to be more war-like than Zabrak from their colony worlds, most likely due to the rugged terrain that made up their home world. As such, they developed a highly physical style of martial arts, which were a requirement for young Zabrak to learn. It was not uncommon for Zabrak from Iridonia to be among the best hand-to-hand fighters and weaponsmiths in the galaxy. Zabrak from colony worlds also shared that drive for excellence, but encouraged their children to express it in other ways. It was thus not surprising to see that the Zabrak met with success in many fields, ranging from medicine to entertainment. 
Zabrak would commonly take their names from animals native to Iridonia, with many Zabrak families named after the Bukk. Many Zabrak males were named after the Blok, Lok, and Zur. Many Zabrak females were known to take their names from the Triz.
As one of the earliest spacefaring species in the galaxy, the Zabrak played a major role in Galactic affairs. Like the early Humans, the Zabrak established many colonies outside their home system early in their history, such as on the planet Iridia. The Elomin species was believed by some xenoarchaeologists to be descended from Zabrak colonists who settled Elom in the distant past. By the time the Zabrak encountered the Republic, they had a total of eight colonies in five systems. 
Long ago, the Sith had made contacts with the high council of Iridonia in order to hire the services of their most talented mercenaries. This influence remained with the Zabrak people long after the Sith were thought to be wiped out, though it remained more closely associated with the Zabrak of Iridonia than the Zabrak of their colony worlds. 
References:  - http://starwars.wikia.com/wiki/Zabrak