Mare, why not try and cross AMS with another mold resistant, early flowering strain. If its for outdoor you should be trying to make your bud flower earlier and be more mold resistant, not cross with a new strain to make it less mold resistant. There are some strong strains that aren't prone to mold, but I'm not sure about early flowering and mold resistant. The one I was going to grow this year is ATA Tundra, it is supposed to be mold resistant, early flowering, resistant to cold, and really high in THC, but my seeds got stolen. I don't know if everything the seed company claims is true, but it sounded like the perfect MI strain.
KB- Maybe your purple branch is really dank, but sometimes if its not caused by the cold, purple can be a sign of stress or other bad things. Also last year, at the end of the year for me, several of my buds turned purple, and those were the worst tasting nuggz. Hopefully your branch is purple in a sticky dank way and not purple in a bad way.