You gotta use a loop/pocket microscope to look at the Trichomes (crystally resin glands) on the buds and leaves... the red hairs are different for every plant, some stay white the whole time, some turn brown, some are blue and stay blue... but they're a bad sign of your plants maturity... trich's start off clear, then gradually turn a cloudy white/milky color, then they get an amber tint... when they start turning amber is the "ideal" time to harvest, but if you pick earlier the high is more energetic and if you pick it later it's more couch lock... if you pick too early you will be VERY disappointed in your smoke, take it from someone who's been there! goodluck!