The oldschool method, before using a scope on the tricomes was to judge by the amount of colored pistils. So the 'happy place' was to harvest when you had around 75% colored (any color but white) pistils. Also, you want to base this count from the more mature colas, not the lower side colas. And, don't forget to use the whole cola, even the bottom part of it that will contain more amber/red/brown pistils. Now the current science points to inspecting the tricomes for a milky and amber color, with the majority being milky, and 5-10 percent amber. They say the milky is where all the thc is, so as long as there are not a large percent of clear tricomes, it's probably ready. Last but not least, I've read that there is basically a two-week window to pull them and the rule of thumb is if you think they are ready, wait one week and then pull them as you will certainly be in that window.