I've always had a healthy amount of yellowing during flowering, but this plant is 6 weeks in, and has such healthy leaves, it's amazes me. I don't know what I did right, but I gave it the same feeding regimen, as it's mother got last grow. There's only a few leaves that are still bright green, but slightly faded, not a ONE leave has fallen off, and there is a LOT more crystals than it's mother had last season. I can't wait to see what I pull off of her come harvest!
the reason plants go yellow isnt because the grower isnt feeding them right... when you grow cannabis, on the last week you flush all the nutrients out of the soil, this helps the plant break down slightly, and tastes MUCH better...

you can either go for a big yeild with crappy, harsh tasting buds, or you can sacrifice a small amount of yeild for a better taste... or, you can try to find a good balance...

personally i flush... but do whatever you like...