cold isn't the only cause of purple bud... i'm not so sure on strains and if GDP is one or not, but there are strains that are genetic (since i'ts in the name, i'm going to go out on a limb and guess this is supposed to be one) but i'm not a grower, so don't take my word for it, atleast the last part... the other part i do know, and you can take my word for it.