Class distinction in the 18th century was of importance and wigs were used to make the distinction clear.
Men in a professional occupation typically wore grey wigs, men in a trade type job wore brown wigs and white wigs were reserved for judges and military officers and our Founding Fathers.
If you were of great importance and could afford it you would have a few wigs for daily wear, one for riding, one for a night out on the town and so forth.