yeah, wait for the pistils to start to coil up. shouldn't be long.
can always harvest the top colas first and let the lowers ripen more, too, if there is any deviation in development top-to-bottom, which generalyl is the case.
that way you don't have too early lower or too ambered up tops.
trichomes
pistils
density of colas. - use this one sparingly when the others point toward immediate harvest. no reason to fondle the plant more than necessary.
use more than 1 metric. you'll moer consistently choose the same point in ripening process. some strains won't show amber much at all even if you let it die on the stem.