It's sort of like taking a sample of a massive population. Of course you can never sample each and every person of a huge population, but if you pick lots of people from the population you can get a pretty good general idea of what the whole is. Same goes for trichomes. Of course you can never see them all, but if you take enough samples from enough buds, a picture begins to emerge and in each sample you will begin to see a reoccuring pattern, whether it be that almost all the trichs you see are mostly clear with some cloudy, mostly cloudy with some clear, or whatever the situation may be. You just have to look at all of your buds, and guage what the reoccuring and dominant trichome color is.