It's natural for there to be some yellowing off of leaves at the end of flower, don't give it any nitrogen whatsoever. The plant is using up all of its resources at this point, what do you have 1 or 2 weeks left? The hairs turning red are an indication that maturity and end of harvest is here, however it's vital to wait til the trichs go cloudy, I like a little amber too myself. Be patient and at this point don't worry about yellowing, just keep feeding a mild late flower feed to them til the trichs cloud up.
Take a few samples of the sugar leaves off and take them out of the flower tent to some good daylight(6500k) light to check em, I even like to use anything black to look at them on, so the light doesn't play with your eyes or reflect white back at you, look at all the trichs and compare them, til you get used to seeing the difference it can be a bit tricky to tell. There will be some really clear ones and a couple cloudy at first, then more cloudy, and the ones that were cloudy before turn amber, that's when I like to pick! Hope this helps