this comes from personal experience when a older took me to a weed farm and the way to tell is..... stand back from the plant is there a gold tinge from the tri's ? and have all your beautiful white hairs turned orange yet ?
note - as a massive smoker of herbal (not medical, not legal, total smoker joker in the UK) i will only place my hard earned cash into the hands of sticky, red haired weed.. keep that in mind
Well the red hairs are not really the best way to tell mate. Some strains are ready when half are red, some 80 percent, some all of them. If you harvest and dry a bud with even 50 percent red hairs, odds are they will all go red in the drying process anyhow. You have to take 'em REALLY young to actually have those yellow immature stigma on a dry bud. As a matter of fact, the 'orange' hairs are usually the white ones, if they go red on the plant odds are you won't even really see them on the dry bud at all. This has been my personal experience so it is my opinion only on how it goes, but outdoors I have had a few crops forced early and left one waaay too late too, so I've got tons of grounds for comparison etc.
'Ready' with reefer is not an absolute, a lot of it boils down to preference also. Rule of thumb is, a trich turning amber is actually starting to degrade, so once the majority start heading that way (turning milky with around 10 percent amber trichs) your plant has reached asbsolute peak cannabinoid levels. That's harvesting for peak potency. Peak flavour, wait a week. More than that and it becomes over-ripe, noticeably weaker, doesn't store as well, etc...