Heyy ccore! You have nothing to worry about there. That just looks like the plant doing its thang and changing colors as it get older plus the 10*f temp swing between day/night also helps bring this out in plants. It's a good thing to have that temp swing it mimics what it would be like outside.👍So nothing to stress out over this is a genetic thing some will do it more than others the plants look very healthy by the way nice job.👊 hope this helps! Happy Growing