That's very much up to the plants genetics, how you've cared for it, and what your preferences for a high is about.
- Like the other guy wrote tho, a jewelers loupe, or equivalent magnifying glass, with 50 - 60x zoom, will help in determining how the trichomes look.
- Don't listen to him saying "10% amber tho".. That's entirely up to you. It will depend on how you want your high.. Personally I prefer as much amber as possible, as I want as much of a stoner as I can get, so I'll harvest later than most people. If you want less of a stoner, and more of an energetic high, harvest with less amber, since the more amber, the more stoned you'll get. Which means, you can harvest earlier. Tho, some strains start producing amber right right away, so you'll get a stoner nontheless. Just remember, that clear trichomes won't give you a noticable high at all.