Only thing I know of is PurpleMaxx from Emerald Triangle (Humboldt County's Own).
For what's it worth flower color has very little to do with additives. Start with genetics, then dial in environmental conditions for "Autumn" colors, lastly is the PurpleMaxx. I've never used the stuff myself but I hear good things about it and I do use Gravity. The stuff is powerful, less is more. Like .5ml per gallon.