Ask these questions to your suppliers. PP copolymers come in many grades and melt indexes and the processing temperatures need to also reflect the L over w ratios you have in your molds. I usually start around 410 F and go from there.
Your colorant house knows what will happen to the color if you over heat it. They should have been informed by you the plastic you were intending to color and should have provided an adequete color concentrate in a compatible color carrier resin. If they did not, maybe it is time you tried another color house.
Plastic Consulting by the hour. PM me