They fade more when they’re not getting the nutrients they need. It could be from cold temps, pH, stress, overall lack of nutrients, or whatever. Genetics also play a big role in the colors.
I just posted this a couple days ago. It shows one of my organic no-till pots next to a coco with GH Flora. Both Love Affair clones. The organic started showing P deficiency so I added guano, but I was a little late. Hence the purpling.