Red Pavilion, and the Green, Ebony and Blue ones before her). S stands for Sandalwood. The color of sandalwood can range from dark reddish-brown to neutral beige hues, through a series of different softer shades of brown. In addition, sandalwood is a scented tree, often used in many Eastern cultures, which is probably why the Thursday pavilion is called the Sandalwood Pavilion, rather than just plain Brown.
The Chinese Princess (actually the text calls her "Chinese Turk" and in some translations "Tartar") in the Sandalwood Pavilion tells Bahram Gur the following story:
Fortunately for Good, a Kurdish tribe happened to pass by, and the chief's daughter found him. She put his eyes back and healed his wounds, and the Kurds took him in, slowly nursing him back to health. He married the girl that saved his life, and started a family of his own. One day he came across a sandalwood tree, and gathered some leaves, knowing they could cure many diseases. He kept the medicine a secret until he heard that a king nearby had a daughter on the verge of death; healing the daughter, he received her hand in marriage as a second wife. Healing with sandalwood proved to be a lucrative business: He did not only end up with three wives (two of them princesses he saved and one that saved him), he also became a king in his own right, and ruled over a country for many years. One day Bad showed up to pay the court a visit, not knowing who the king was; when he found out he begged for forgiveness, and Good forgave him for his crime.
The Kurdish father-in-law, however, did not. When Bad left the court, he followed him, and cut off his head.
The story ends with stating that Good, when he became king, wore sandalwood-colored clothes only, and decorated his palace with the soft colors of the sandalwood, to remind himself and everyone of the healing power of the tree, and the adventures he lived through.
If you are keeping count: Two more princesses coming up before the end of the month (White and Yellow). Stay tuned!