From Holocron - Star Wars Combine
|Average Height||1 - 1.5 meters |
|Skin color||Green (exposed skin at snout) and orange (at jawline) in ultraviolet light |
|Hair color||Blue to yellow in ultraviolet light, black to dark brown in visible light |
|Distinctions||Absorption of visible light, light-blindness, claws |
|Average lifespan||90 years |
|Known Members||List of known Defel|
Biology and Appearance
The Defel are a wraith-like race that absorbs normal light through their fur and skin, appearing to be nothing more than a shadow. In ultraviolet light, they appear as short, muscular lupine humanoids with thick fur and unusual, three-jointed fingers. They live underground on the planet Af'El, mining the various metals in the planet's crust and outer core. They can see equally well in normal and ultraviolet lighting, and their eyes appear to glow red in normal light.
Since Af'El had no ozone layer, ultraviolet light passed freely to the surface, while other light wavelengths were mostly blocked by the heavy gases in the planet's atmosphere. Thus, all lifeforms on Af'El could see in ultraviolet light ranges, but were blinded by all but the dimmest light in other wavelengths. This is why Defels normally wore a visor when they left Af'El, and expected to be exposed to daylight at their destination. Compared to other species, they could see exceptionally well in the dark.
Defel were short, stocky beings, averaging 1.3 meters tall and nearly as wide. Though they were nearly invisible in normal light, Defel were actually colorful beings. Viewed under ultraviolet light, their fur appeared in colors ranging from yellow to blue. Their snouts appeared green, with orange, gill-like slits at the base of their jawlines. Elderly Defel lost their ability to absorb light, fading to a dull dark brown under visible light.
Society and Culture
Due to the harsh conditions of Af'El, Defel had a society based on communal resource sharing. Co-operation was vital for survival. As a result, the typical Defel was a tough, independent being, with a strong sense of honor. Defel stood by their word, and refused to associate with anyone who broke a promise. The Defel lived in underground cities to escape Af'El's violent storms. Their subterranean society had developed highly advanced mining and metallurgical technology, though they had not developed space travel or agriculture on their own. 
Common Defel names: Dourlas, Freel, Gr'vesh, Yarchur 
Their homeworld was seldom visited due to the difficulty of escaping its gravity well, making Defel rare outside of the Ka'Dedus system. This rarity, combined with their unusual abilities, meant that much of the galaxy believed they were mythical or supernatural beings. Some of the few Defel who left their homeworld went in search of adventure, and often employed their natural stealth abilities to become assassins, bodyguards, or thieves. Most Defel who left Af'El, however, were prized more for their skills in metallurgy, and were contracted by smelting operations and starship manufacturers. 
The Defel did see some trade in meleenium, a rare substance used in durasteel production, which was only found naturally on Af'El. During the Imperial era, Vulca Minerals sent one ship a year to the Defel to trade fresh food for meleenium. Under the Empire, Defels were oppressed. 
References:  - http://starwars.wikia.com/wiki/Defel