All of this comes from the Essential Guide book published back in 2001.
Falleen are reptilian humanoids that occupy the Falleen star system. They are a handsome species exotic in appearance with scaled, gray-green skin & a spiny, sharp ridge that extends down the center of their back. This ridge is indicative of their reptilian nature, as is their ability to change skin color. Female Falleen look slightly different from their male counterparts, in that the spinal ridge is smaller, their skin is lighter, & the ability to change color is somewhat more limited than in the male counterpart. Unlike most reptilian species, Falleen grow hair. The females like to wear it long & adorn it with combs & beads. The males wear their hair ties up in a single braid or topknot. In recent years, some females have taken to wearing topknots, in an effort to attain the same elevated status as is enjoyed bye the males. This species is considered aesthetically pleasing by most humanoids. Although their physique is perceived as well defined & attractive, the wide spread acceptance they enjoy is not soley based upon appearance. They, like the zeltrons, can exude pheromones at will, & these chemicals are used to control the perceptions of others-perceptions that the Falleen frequently manipulate to their advantage. The Falleen are also a long-lived species, living 250 standard years on the average. Some healthy individuals have been known to live 400 years. Falleen pheromones are so powerful that they can fully produce an almost hypnotic effect, & the manipulations often take on lustful overtones. What also makes the Falleen attractive is the aura of mystery in which they have wrapped their selves. They are not a talkative species & tend to be pensive. They do not show emotion in public, they maintain a great deal of control over their physiology. Culturally, they remain stoic & shun outward signs of passion & anger. They experience emotion, but simply don't show it. As a result, the Falleen regard beings who do show their emotions to be inferior.
They also have harnessed the ability to control their skin color & have learned to use it as a covert weapon, reverting to use their normal shades of gray-green to red or orange, for example, in order to exude an essence of confidence or mastery. They use their pheromones to enhance the effect & further make a subject susceptible to suggestion. Pheromones may also be used between Falleen as communication tools, although they always suspect duplicity & remain disciplined in order to resist suggestions that may be imposed upon them by others. While the Falleen have employed space travel technology for generations, they rarely venture to the stars. Because they consider the Falleen system to be the bastion of the galaxy's greatest culture, they prefer to manage their own affairs on their homeworld, rather than deal with offworlders. Their music, sculpture, & architecture provide a source of great pride for them, although they rarely share them with offworlders. Falleen society is feudal, with noble houses ruling lower classes of artisans, technical workers, general workers, & slaves. Monarch rulers govern their kingdoms, caring more for internal political intrigues & the display of their wealth, rather than wasting resources in a raging warn against each other. These kings maintain commerce with one another & occasionally argue over boundaries, although boundary disputes are never taken to extremes. Young Falleen nobles will sometimes spend part of their adolescent years on what is called a pilgrimage, a tour of the Galaxy that allows them to experience all it has to offer. Most of them return to employ what they've learned when the time comes for them to ascend the throne. One prominent Falleen was Xizor, whose entire family was killed at the hands of the Empire. Darth Vader had order a biological weapons lab to be built in Xizor's home city, & when a lab accident contaminated the area, Vader ordered that the city & it's 200,000 inhabitants be burned to ashes. From that point on, Xizor retained a deep desire for revenge against Darth Vader. He rose to lead the Black Sun crime syndicate on Coruscant, plotted to kill Vader & take his place by the Emperor's side. His ambitions, however, led to his death at the hands of Vader, the man he hated most, when Xizor overstepped his bounds & threatened Vader's son, Luke Skywalker. The dual diaster of biological contamination & a brutal orbital strike to "cleanse" the infected city convinced the Falleen to remove themselves from all involvement in galactic affairs. For this reason, even under the rule of the New Republic, the Falleen are rarely ever seen traveling outside their system, & they have shown no desire to join the new galactic government.
Thanks for reading & MAY THE FORCE BE WITH YOU!