Yes, it is true. Colder temps, less than 65F during the later stages of flowering can increase the likelihood of the leaves changing to purple or blue, but it has to be in the plants genetics too to some point. Not every strain will do it, just because it is subjected to cold. There is no benefit other than bag appeal to an unknowing buyer. Cold temps can however help in trichome production, but there is a point of detrimental returns, where you go to cold and hinder production.