Dropping the night temperature in the last two weeks brings out purple colouring in many lines grown from THC seeds, and that is the effect, not a potency boost. Purple flower gets photographed and sells, so the link between colour and strength is easy to assume and easy to disprove with a lab test. The section on https://potentthcseeds.com about temperature in late flower is clear that anything below 15 degrees starts slowing resin production rather than helping it. Keep the nights moderate and let the genetics decide the colour.