its been said, Ill reasure you; hairs have nothing to do with maturity. A wide variety of factors can make your pistils die...ranging from nutrient overload, high temps, lack of circulation, etc. I have had grows where only about 25% of the hairs changed color but the trichromes were majority cloudy with a small amount of amber trichromes. Ive also had other grows where the pistils were nearly 85% dead but the trichromes just became mature.

A lot of dead pistils early on is usually an indicator that your temps and/or humidity are too high or that your plant is going hermaphrodite.

A 30x microscope is really enough to see, but a 50x is better. Like its been mentioned, there are 3 distinct trichrome maturities. Clear, Cloudy, Amber. Everyone has their own take, but its generally said you want majority cloudy with a few amber. Wait to long and your dank will lose potency and be more of a couchlock. Harvest to early and you will not have achieved full potency and the high will fade to quickly.

Practice makes perfect. Harvest most at one time, then leave a few so you can try the difference for yourself. Its not as if picking early or late wont get you high, but when you put that much effort into a grow, put the final effort into harvesting at the perfect time. I personally like just majority cloudy (whether there are a mostly cloudy and a few clear or mostly cloudy and a few amber doesnt matter to much too me).