well first do your research cause purple punch/power is a nice hybride.. purple punch is a 60/40 indica and power plant is a 70/30 indica so it is a good mix.... there is a chemical that botanicare makes called florilicious and if used as a folar spray will turn any bud purple... but natural purple is the best... basically by the 5th week your plant starts to lose it's green pigment in the leaves which in return turns your plants purple