When to harvest is a lot dependent on how you like your smoke or as most would say the “kind” of high you like. Clear trichomes will give you the clearest “head high” (buzzy)…opaque white will give you a combo of head and body, and amber will give you the most body “couch lock” type of high. Most perfer harvesting when there are around 10-20% amber trichomes on the seed brachs. But the type and intensity of high is also very much dependent on the quality and of the strain you grow. They all make trichomes and they all change color, the difference is in the genetic potency of the plant.