Is it normal that the leaves are getting this colour?

https://420life.com/wp-content/uploads/2021/10/Marijuana-Leaf-Deficiency-Chart-scaled.jpg Kinda looks like a P issue. But your also almost done so could be a bit of fade? Also the feed has lots of P in it so it should not be deficient at all. Bloom 4ml 12-36-12 / Boost 3ml 9-10-38 = 10.7-24.8-23.0 NPK ratio. Ton of P. almost to much. Your suggested feeding for the nutrients used is here : https://420flow.de/cdn/shop/files/FINAL_V2.png?v=1713467798&width=1000 This is also a good tool. https://www.nutriag.com/wp-content/uploads/mulders-chart.jpg Its shows high P requires High Mg as well and can make issues with Ca. I would monitor the EC of the solution and back off some of the feeds as it nearing end of life. Also do any of them feeds say their micro content? Eg. Fe, Cu, Zn, Mo, Mb,?? Also you are getting a good amount of runoff when feeding them yes? if not it could be a build up casing issues.

It is absolutely normal for late stage flower to develop dark colors in the leaf. A lot of places are actually breeding that into the plant because it’s turned into a desirable look. I did a quick search for the RS11 plant and it looks like the majority of all the end of flower plants have a very dark purple leaf. I would say you are right on track and keep doing what you are doing. It should turn some lovely color by the time you are ready to harvest. Hope this helps.

Purple genes in first two and last. Fade and lack of phosphorus in third photo ... but its all in natural phaze of canna plant. Would not worry about anything !