NPK Deficiency?

That's is definitely lacking in nitrogen the yellowing of the leaves is her searching for nutrients as you can see these are beautiful large flowers and at this stage shes trying her hardest to make them even fatter for you and the yellowing is actually kinda good its showing that she actively seeking out nutrients to pile on the pound on them flowers for you so advice give her what she wants. Up your nitrogen in your feed. yes the plants don't need much N at this stage but Nitrogen like the P and K are mobile nutrients meaning they are in constant use by the plant regardless of which stage you are in obviously in different stages they need different amounts of each nutrient but they are constantly using NPK. Though these plants look amazing and depending on how long they have left in flower then you could use this to your advantage when it comes to the flush but to me I would feed her and I can guarentee you will probably add an extra 50 or so grams to your final yield :) Hope this helps bro. But if you ever see yellowing most of the time its going to be nitrogen she is actully trying to eat herself in order to pump up them flowers more :) best of luck for the finish and you should be proud of growing such beautiful plants :) Oh and purple is classic smyptoms of phosophrous defienceny which is defenatly needed the most at this stage :)