Silk Description
Yellow Tavern owned slaves or Camp slaves, can be used by Any Masters of camp, if the Leader of the Camp is shown great respect in return. Yellow silks cannot yet train others, and are still in training themselves, but to the stage where they can "practice" that training and improve on it. Practice in the sense they can serve food and drink, improving on their skills, and to be "used" by a Master of GDC means they may serve in the furs with ONLY a Master of GDC, None Other without permission of the Ubar or their personal Master.

Too, Ina wore a snatch of diaphanous yellow most paga taverns, of course, the girls are silked. Usually it is only in the cheapest and lowest of taverns that the girls serve naked....Slave silk, and certainly that sort which is commonly worn in paga taverns and upon occasion in brothels, when the girls are permitted clothing there, is generally diaphanous. Dancer of Gor, pg 224

She was clad in in a snatch of yellow slave silk..... Vagabond of Gor, pg. 400
Red a silk given to a pleasure slave. A pleasure slave is trained in all sexual pleasures, in service and in dancing. Sometimes used only by their own Master and Those He holds in trust. atia, though a red silk, is sexually, for her Master's use only, by His command. Red silks may train other slaves.

"There is a stain on your thigh," I said. "My Master took my virginity," she said. "You are now a red-silk girl," I said. "Yes, Master," she said, "I am now a red-silk girl." Explorers of Gor Page 200
White a silk given white silks, is either a virgin or one whom her Master or Mistress is not willing to share with Others. she is only allowed to serve drink or food, and engage in conversation. Any who violate the sacredity of the white silk, is set for a sentence of death at the hands of the Master/Mistress who owns the white silk. Can train other slaves if their Master/Mistress allows.

"Are you white silk?" I asked. "I am a virgin," she said. "Then you are white silk," I said. Explorers of Gor Page 172

The meal was served by slave girls in white tunics, each wearing a white-enameled collar. These would be girls in training, some of them perhaps White Silk Girls, being accustomed to the routines and techniques of serving at table. Assassin of Gor, pg.88
Gray State-owned slaves.

"They wore the brief gray livery of the state slave of Ar, slashed to the waist, knotted with a gray cord; about their throats was locked the gray metal collar of Ar's STATE SLAVE; they were barefoot; on the left ankle of each was the gray metal band, with its five gray bells, worn by the female state slave. Their hair, in state fashion, had been cut short, shaped, and combed back around the head. The wrists of each were confined behind her back with gray slave bracelets." Pg. 398, Assassin of Gor.
Purple slaves who serve the Priest Kings.

"Among them i saw men and women, barefoot with shaven heads, clad in short purple tunics thaat reflected the various lights of the plaza as though they might have been formed of some reflective plastic." Tarl Cabot describing the slaves He saw while with the Priest Kings in "Priest-Kings of Gor; pg. 90
Black kettle slave, owned by the camp, but no individual Master, cannot train others, may only cook and clean while training for yellows, lest in testing.
"I wore the belled collar, and belled ankle ring, of the tavern, and a bit of black silk." Pg. 340; Slave Girl of Gor.
Blue this was mentioned several times in the books, in different was, several times in regards to dancing girls.
"'I had intended to rent a dancing slave in Vonda,' said the Lady Florence to her guests, 'a decorous girl in blue silk and a golden collar, who might by the loveliness and grace of her movements please us, but it slipped my mind.'" Pg. 287; Fighting Slave of Gor.
Brown it wasn't really specific what these silks were, but they were mentioned in a couple of books.
"She wore a brief bit of transparent brown slave silk, gathered before her and loosely knotted at her navel." Pg. 393; Beasts of Gor.
Gold mentioned once in regards to a tunic of the southern area.
"The silk girl was heeling her master, a captain of Torvaldsland. She wore, indeed, a brief tunic of the south, of golden silk. She wore a collar of gold, and, hanging in her ears, were loops of gold." Pg. 145; Marauders of Gor.
Green this was mentioned in regards to pleasure slaves.
"The Pleasure Slaves who served wore green pleasure silk, and the tops of the tables and the walls were also painted green; even the curtains on the alcoves by one wall were green." Pg. 167; Assassin of Gor.
Multi-co lored this isn't specified either, but possibly used for dance or just enticement because of the coloring.
"The girl ran to my side in a swirl of many-colored silks and from beneath the Robes of Concealment she withdrew my sword and kneeling at my side lowered her head and placed it in my hand. “Cabot my Master!” she cried." Pg. 266; Priest-Kings of Gor.
Scarlet sometimes used as dancing silks, mentioned several times in the books as such.
"As I mused, Talena stepped forth from behind the silk curtain. I had thought she had retired. Instead, she stood before me in the diaphanous, scarlet dancing silks of Gor." Pg. 134; Tarnsman of Gor.