How can a man pull of wearing white briefs?

The reason why underwear is often white traditionally is because the purpose of underwear was to keep outer clothes cleaner longer so that only underwear needed regular washing and outer clothes needed less frequent washing. Before washing machines and dry cleaners, this was obviously of huge importance in terms of time and money. Because of this purpose, underwear was boiled and bleached to clean it, and you cannot boil and bleach clothing in colors other than white. Nowadays, underwear is available in all possible colors because modern washing technology and detergents make it unnecessary to boil and bleach underclothes (although bleaching underwear is still common, and when this is done white fabrics are preferred).