Trichomes - starting with at least 5-10% in multiple locales inspected (calyx one, not leaves)
Pistils - color early on usually at least 50% but varies a good amount -- later on in window they actually coil up.
Density - do this only to further verify choosing to harvest... give one nug a little squeeze without doing much damage..
Use all three to determing harvest. If new, experiment with early middle and late. Whatever you think you prefer, aim to harvest the bulk then, but you could always take samples over 7-10 days and have no fears of nanners forming in that time. you might even take the bulk at any stage, but leave enough to ripen and test as they amber up more... this way you can have a better idea of what you prefer... expect some variation by genetics of course.
One of the better fox farm trio finishes i've seen. Some minor tip burn, but it is good to be on that edge. full disclosure: i have a bias against FF trio and it's' not good-natured. lol, jk it is mostly good-natured. if it works, it works ... bottom line.
The canopy is still green because soil just keeps on giving, No worries. Feeding or not does not impact the molecular makeup of buds. They are not storage facilities. They are sex organs made to do one thing -- reproduce. keep it healthy until you harvest and if it pales by then, no big deal either. It'll start sucking the leaves down within 1-3 days in soilless and almost immediately upon a reservoir change for hydro. Soil takes a bit and will vary based on how you fed and what's self-propogating in soil, if anything etc etc... just more carryover all over. microbes still breaking down stuff in soil before it can be taken in by roots etc etc...
you don't want drastic changes to EC, imo. The plant works alot with osmosis, which depends greatly on 'normal' concentration gradients to function properly. plenty of evidence and blind taste tests are piling up against any causality behind flushing at end of harvest. Either way, what you choose won't make much of a difference is the key to that question.