White Tea is essentially unprocessed tea. White tea is simply plucked and allowed to wither dry. If the weather isn't cooperating, the leaves may be put into a dryer on very low heat to assist. Some minimal oxidation does happen naturally, as it can take a full day or two to air-dry the tea leaves.
This is why some white teas, like the Pai Mu Tan shows leaves of different colors (white, green and brown). White teas produce very pale green or yellow liquor and are the most delicate in flavor and aroma.