There is no specific prescription for what Buddhists should wear, although they are referred to as "lay disciples dressed in white" in Odatavasana, A.III,10 and M.I,340. Buddhist monks and nuns, however, are required by tradition to wear naturally dyed robes.
Sources for the robe dyes are limited by the Buddhist scriptures to root, tubers, plants, bark, leaves, flowers and fruits. The most common colors today are saffron and ochre, the latter of which is sourced from the jackfruit's heartwood.
Often forest, or rural, monks will wear ochre while urban monks will wear saffron; however, there is no specific rule guiding this tendency.
The Buddha himself wore a yellow robe, but advised his followers that far more important than their clothing was the quality of their hearts.