NEVER! AND I MEAN NEVER harvest on the colour of the pistilles [hairs]

They mean NOTHING.

You harvest depending on colour of trichomes - which will tell you when the THC is at its maximum - and then you can harvest to your liking for the high/stone you want.

Clear trichomes - not mature
Cloudy trichomes - mature
Amber/ Cloudy - perfect time to harvest.

Just make sure you havnt got too many ambers, as this is when the THC degrades into CBD and CBN - which will give you a more indica like stone.