It doesn't appear to me to be anything beyond a simple lack of N from the switch to flowering ferts. A dose of veg ferts in place of the flowering ferts for an application or two won't hurt then give it a couple days and tell us how they look. Expect to see more yellowing of the fan leaves as the plant ripens, especially the last few weeks but it is a bit early now to have that much yellowing. If they were mine I'd also add a little "Dark Energy" as a supplement to the ferts.