I honestly I see very little correlation between color and potency. Yea I have had a couple weak purple strains, but I have had just as many weak green strains too.... I have half a dozen people that ask for the Plush regularly and swear its the best shit they have ever smoked! My cut of purple kush will put yer dick in the dirt! Couch lock night-night time after half a blunt.
Now double purple doja, a gorgeous heirloom purple strain, although beautiful & frosty, is only maybe 6/10 or 7/10 potency. But she is used in alot of crosses, and is AMAZING breeding stock