Yeah, you shouldn't rely on any one sign too much. If it is still putting out new white hairs, it's probably not done yet, even if some of the trichs are turning. By the same token, it's also probably not done if all the hairs have turned brown but the trichs haven't turned. Another good sign is the yellowing of the lower fan leaves, though that can easily be confused with nutrient/pH problems, so it definitely isn't a reliable factor on its own.
It's hard to recognize the signs your first time, but after awhile you'll get the hang of it and just have an intuitive sense of how close the plant is to finishing based on all those factors, though obviously plants vary from strain to strain. Just as an example of what finished bud can look like, here's a plant I grew back in 2003, which shows the browning of all the hairs and the yellowing of the leaves:
As far as a microscope, I just have a camera with a zoom lens, so I take macro shots to see what the trichs look like. But if I didn't have that, I wouldn't spend too much money on a microscope. You can kinda tell the color of the trichs just with your eyes or a cheap magnifying glass, assuming your vision isn't terrible.