Hey. Wow, I love it, it's stunning. I'm going to answer your question.
At this stage of flowering (Day 70), it's completely normal and even a very good sign.
Anthocyanins: With the drop in temperatures (especially at night) or simply with genetic maturity, the plant reduces its chlorophyll (green) production to make way for anthocyanins (purple pigments).
Senescence: It's autumn for your plant. It's mobilizing its last strengths and nutrients towards the flowers, which changes the color of the "nourishing" leaves.
2. Problem?
Not at all. This is not a deficiency. If it were a phosphorus deficiency, the stems would be very red and the leaves would have dark, dry spots. Here, it's a clean and uniform gradient that often starts from the edges or the top. It's pure "bag appeal" (it's going to make your buds look amazing once dried).
3. What it tells you about the harvest
Critical Plus usually finishes around 60-70 days of flowering (depending on the phenotype).
The signal: This coloration confirms that the plant is nearing the end of its life cycle. It won't grow much more, it's fine-tuning its resin and terpenes.
Flushing: If you're in soil and using fertilizers, make sure you're well into the flushing phase with clear water so that these colors intensify and the taste is as pure as possible.
My opinion: Don't change anything about your parameters. Enjoy the visuals, keep your humidity nice and low (below 45-50% to avoid mold in those big dense buds), and get ready, the big day is approaching fast!
I wish you all the best, and it's still super beautiful. Have a great weekend!