I agree with Creepy_Steve, a lot of trichomes stuff is little bit dumbed. Before, i was using a magnifying glass x30, i suggest you to buy one if u wanna recolt at the perfect moment. But honestly, that depends on the genetics you grow, and imo, this is better to harvest for high potency THC, rather than wait for an amber color, because more you wait, more you loose these good terpenes and stuffs... so.. everyting is with your instinct, after some experiments, you know when the plants are ready, without using the magnifying glass. Check the buds, density, when this is dense, trichomes are milky, you can think to wash the roots. This is my way of working, after many harvests.