IS it normal ?

Yup. There's a long name for what it is, or 1 I just can't remember. Ppl just call it the fade. Some strains like runtz, purple punch have a certain amount of "........", some plants show it mid-late flower. But a lot of plants, most actually have tiny bits of fade. Even my green leaf zkittlez has some purple on the sugar leafs. Mainly on the back. I've seen zkittlez also be black. You have to have a decent swing in temp to show the full terps of a plant with lots of fade, as I call it. Sadly I don't have a cold enough house nor can I create big swings in temp during flowering cause my dehumidifier control temp. You seem to have a decent swing in temp, you must have a dark period do you, I haven't looked? Anyways, I'm rambling, this your question sry. 100% normal bro. Good sign your plant is showing her full pheno/traits if you will. Sit back and watch her grow. What she's about 20-25 days in by the look of her. Still a good 30days to go. Maybe less depending how you like em. Good luck.