Do not, I repeat do not be drawn into the common misconception that "purple," "purp," or "grapes," is better quality dro than other strains and kinds. Photosynthesis in marijuana is done by both green and red chloroplasts, depending on the strain. When a plant reaches maturity, the plant stops new cell growth, and the green cells begin to die. For those plants that have red/purple chloroplasts, the purple color beings to show. Strains named "purple" for example grandaddy purple, change at slightly higher tempuratures than other indicas, but 90% go through color changes anyways.

Bottom line, The purple color has no effect on THC production, it is merely triggered by low temperature and late in flower.
compliments to Cannabis Culture Magazine for fillin in.

However, purple does carry some auroa of authority as strains that do have a tendancy to turn purple can be quite chronic if grown correclty.

On an endnote, there are ways to tell the quality of your bud. Good bud should smell pungent and pleasant, and should burn evenly and smoothly. I always feel the texture of my bud, making sure it is slightly springy and not to brittle.

In all, dont overpay for bud simply becuase it carries the tittle "purple." Shitty weed can be purple too.