However, plants are frequently seen with foliage of a variety of other colours from shades of red, brown, purple through to black. These colours are caused by other pigments such as betacyanins and anthocyanins produced in response to environmental stress, as a mechanism for filtering intense sunlight or as the endpoint of selective breeding of desirable cultivars. These pigments are incidental to photosynthesis, but may well only be produced in plants grown in the strongest light especially with a high blue and ultraviolet content.