taken from "tea: Aromas and Flavors Around the World"
The processing of yellow tea begins in the same way as Chinese green tea, expect that the fixing of the leaves takes place under a covering o straw. This is followed by an extended “resting” period under cover during which some slight fermentation occurs. The tea is then delicately rolled into needles and dried. This process gives the leaf a green-yellow color and produces a golden yellow liquor characterized by aromas with a dominant fruity, flowery note.
This tea is produced in only one place, on Juan Shan island in Dongting Lake, Hunan province, China. The most prized of all is Jun San Yin Zen, which consists only of buds. It’s rarity and fineness mean that this quality of yellow tea sells for around $69 per 3 ½ ounces.
And According to Dragon Tea House
"...makes this a yellow tea is an extra step in processing during which the tender white-haired buds are covered with mats which, while not causing oxidation (as in the case of oolong and other darker teas), produces their characteristic pale gold color. The crystal clear brew is pale yellow in color and the leaves stand up vertically like needles when brewed with water at around 85ºC."