There very much are fatigue caps on gathering. Very easy to find if working toward cheevos. All of a sudden things you've successfully pulled out for hours start getting damaged more and more and more til every swing/chop yields a damaged item. That leaves you with half xp and no actual item. To me it is most noticable now with fishing, I barely get into it and already everything gets away.

I'd love some actual numbers, but i realllllllllllllllly doubt that'll ever happen. (at least not from devs) The green/yellow/red is an okay idea to me, but i just stop when half my pulls start failing, I'd call that yellow. lol