ok the best way to get the purple color is to use a hydro system and to add 1 purple koolaid packet to every 1 gallon water when budding starts the cost is only 25 cents per package. I know a guy who does this with his nirvana seeds sweet purple strain and his bud is the sickest purple you have ever seen, the stems are purple and everything just always add the purple koodaid packets durning the whole 2 months of budding during the last week you can change the water out to pure water, but my buddy does not do that he actually drains all the water out for the last week under the lights, no water at all in fact or nutrients, this helps the drying process will go good. Also there is no noticable taste difference. The koolaid my slightly change the ph of the water but a hydro person knows how to adjust ph with no problem anyways my buddy in amsterdam who does this has the best purps ever with a great taste!!!!!
update my friend sent me a picture of what he uses now in amsterdam he now uses sugar-free koolaid he adds 1 packet per 2 gallons of water but you can also add the non sugarfree kind thats onlly 25 cents but the sugar free kind adds a more "purple" flavor to the finished product