Slaves are broken down into two major categories, white and red silk. Simply, white silk girls are virgins and red silk girls are not. The color of the silk bears no reference to their level of training. A White Silk girl could be a fully trained Pleasure Slave while a Red Silk girl could be a new recruit from Earth who did not even speak Gorean yet. No other color silk means anything on Gor. Yellow silks, black silks and the such are online creations and are not based on information from the books.
White silk girls may also be known by the term "glana" but that is usually only used by slavers. A kajira would not refer to herself as "glana." Red silks may also be known by the term "falarina" and its usage is similar to glana. Slave may also be referred to as "opened" or not. If you have not yet been opened, you are a virgin. Virgins are almost never available in the slave markets. Most Gorean men prefer opened women. Virgins present special problems, especially psychological ones. Within these two categories of red and white silk, there are many different types of slaves.
"Similarly, the expression `red-silk,' in Gorean, tends to be used as a category in slaving, and also, outside of the slaving context, as an expression in vulgar discourse, indicating that the woman is no longer a virgin, or, as the Goreans say, at least vulgarly of slaves, that her body has been opened by men. Its contrasting term is `white-silk,' usually used of slaves who are still virgins, or, equivalently, slaves whose bodies have not yet been opened by men. Needless to say, slaves seldom spend a great deal of time in the `white-silk' category. It is common not to dally in initiating a slave into the realities of her condition."
page 472, Blood Brothers of Gor
"Are you white silk?" I asked.
"I am a virgin," she said.
Then you are white silk," I said.
From Explorers of Gor Pg 172
"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.".
From Explorers of Gor Pg. 200