The juice of all grapes, red and white, is almost colorless. The skins of grapes act as a sort of dye. The skins are quickly separated from the juice before the juice begins to ferment. Contact with the skin of a white grape will cause tannins and can make a white wine taste coarse. Skin contact can also cause a white wine to lose its subtle aromas and flavors.
White wines are usually fermented in temperature controlled tanks at a temperature of 50 to 65 degrees farenheit (as opposed to 75 to 85 degrees farenheit for red wines). With white wines, the goal is not to extract color, but to preserve the freshness and delicacy of the fruit, which happens best in a slow, cool environment.