Genetics, Nutrients, Light and Temps can all play a effect on leaves turning purple.
In late flower lots of genetics turn purple.
Light intensity can play a part, ive heard the purple is more efficient then green at using high powered LEDs. Who knows.
Temps, cold Temps can play a effect and many use colder Temps in late flower to pull these colors.
Here is a article I found about this topic. Goodluck, it's probably the genetics.. most growers want this color as it's more desirable product at the end of the day.
Purple cannabis is simply a cannabis plant where the leaves or buds take on purple coloration or shades of purple hue. This is usually due to the presence of anthocyanin, a water-soluble pigment. The more anthocyanin, the more purple the plant appears. Anthocyanins may appear red, blue, or black as well. They often appear in many fruits and vegetables, including berries, eggplant (aubergine), and purple cauliflower.
Cannabis is more likely to turn purple in colder temperatures, as cold breaks down chlorophyll (which is green) and allows anthocyanins to become dominant
Please consider selecting me as the answer so I can be entered for a chance to win grower of the month contest I would really appreciate your support growmie 😃 🙏