Yellow tea is a very rare and expensive variety of tea. Yellow tea is harvested earlier in the year, while the leaves are still buds. That means that the tea leaves still contain all the antioxidants that have been produced throughout the growth process.
Yellow tea is almost by definition a tea that is fermented, or oxidized, for longer than green tea is, but not completely oxidized like black or oolong tea. The drying phase is slower, and the damp tea leaves are left to take on a natural, light yellow color.
By this process, the yellow tea loses the vegetal, «grassy» aftertaste which is often associated with green tea. Many tea drinkers who don’t like the taste of green tea often prefer the yellow teas, as the health benefits are the same, but the taste is subtler and sweeter.