I have sprayed two roofs with Astec products, and temps on the underside of the metal dropped by over 30 degrees on one roof, and 66 on the other (different times of year).
My own, unfinished website is www.energysaviours.com on the "About us" page you can see the difference we made to the metal roof of the "Steamatic" storage building in Beaumont TX. The owner is ecstatic with the results.
I personally love this stuff.
Some of this depends on how much insulation you have and how much ventilation the attic has but thelighter colours do benefit you. White has become passe' partly because of the mildew problem. Stains show and don't look particularly nice.