This is pretty much the first year growing. Gonna start using a 15-30-15. The plant with the most purple had grubs eating the bottom of the roots and was/is very light green and not that healthy lookin.It's pic #2. The first pic is of our biggest girls that we just repotted into 10g root pouches. I have tried to take it easy on the fertilizer. They all have some purpling.
I'm guessing the purpling is just strain related, unless you have a severe P deficiency.
The light green could just be shock damage from the gnawing buggies.
I think after a few grows, or even just a couple, you'll find you have better results if you lower your N during flower, and just occasionally give a shot of veg nutes if necessary to keep them green.
I'll bet that 15-30-15 you mentioned is MG, am I right?
Honestly I think if you go with something like their liquid Flower and Veg food (2-7-7) you'll get just as good results, and not have to worry about overdoing it at full dosage.