or the entire plant becomes light colored.
I didn't say deficiency.. yet.. but its the classic stretch yellowing, 2nd week of flower that many growers see if not feeding properly for stretch..
did you not notice the entire middle plant becoming lighter in color?
The left one is fine but if not fed a good npk it will probably be right behind the middle one, I would not do anything for the left one but feed it as you have, the middle one I would increase the N a little bit 10-20% more and it would only be until stretch is done.
the one on the right seems to be slightly behind the one on the left.
this is my opinion. the op has both our opinions (although you provided no actual advice to them) and others opinions, they can choose who's to use