It's like reveging. You cut off as much bud as you think you can get away with and still end up with a plant surviving and eventually thriving. Make sure you leave some good growth that is nice and healthy, and sacrifice a few of the nicer buds on near the bottom of the plant to be safe. You need a few good leaves to suck that light and make things grow. I end up removing roughly 75% of the plant (mostly AK-47). Any cutting on a plant is shocking it, and how harty strains are is widely varied. Something to keep in mind. Maybe check some seed sellers to find out how harty your variety is.

And hairs turning is not really a good way of determining when to harvest. Get a pocket microscope for $8 and look at the trichomes, then search the word trichome.