it's not the color of the pistils that determine whether or not you should pull it, but rather the trichomes. Pick up a 30x magnifying lense online for like 10 bucks. a jewelers' loupe or wtv. and then look at the trichomes and see if they're clear, cloudy, or amber. If it is clear, then the answer is no.
If cloudy, then it's up to you. If you'd like a more couch locky type high, then let it go on for longer. If you don't like that too much, then cut it when it's mostly cloudy with a little bit of amber mixed it. If you like that serious serious couch lock, cut it at like 50 percent amber trichs.
And for the people who say, "it's fluffy, it's not ready!"......sometimes CFL grown bud is fluffy. If you keep it like 1 or 2 inches away all the time, then yeah, it has the potential to be dense. But a cfl grown bud will most times be slightly fluffier than a MH/HPS grown bud. The only way to determine whether or not to cut is by looking at the trichs, not the hairs, not the fluffiness. Just the goddamn trichs.