yeah exactly it looks like sugar been sprinkled on it. trichs are just like the leaves they form on, the older they are the more you will see amber on them. newer growth will have newer trichs so they will be clear or milky.
there is no "rule" except your own. when the over all average is showing a fair percentage of ambering, thats when i take them unless im looking to keep myself asleep when i cant otherwise then i let them go a bit longer.
mostly clear will get you not much more than a short lived buzz or a headache generally. milky, milky with amber,=yummy. mostly amber means nite nite.
just about any digital camera set to its highest resolution will take a good enough pic to get a better view of the trichs when you enlarge it some.