Good genetics are the way to go for good purple. I never lower temperature myself, but then again half of the strains I have are naturally purple, even at 85F +
Strong purple traits will show in the first week of flower regardless of temp.
I imagine though if everything I produced was green I'd probably lower temp to get some color. For me, I want the effect that most purple buds have - heavy and deep indica stone which often feels a bit more narcotic than other indicas.
Lowering temp just changes appearance. In the summer, I tend to run across purple buds that are what I'm looking for, but in winter it's a mixed bag because it's easy to change appearance and call it whatever, (i.e. saw some Afghan Kush called, "Purple Kush" because it had some purple, which is inaccurate as Purple Kush is a different strain with different lineage).
But hey, if all you want is appearance, why not lower temps?
I guess what I don't like is when people deliberately alter the color so they can sell for more $$ or pass it off as something exotic. To me that's kind of like adding bubble gum flavor to weed and calling it Bubblelicious.
