Sounds like you use a good few factors in combination, I am the same, except I tend never to look closely at the trichomes. In the past it always puzzled me when people use to come out with, "the tricks (because they never spelt it correctly) were 15% clear 78%cloudy and 3%amber, (their strange figures never added up to 100%), either way I was always amazed anyone actually counted anything, or was able too, especially with their maths!!
Sativa leaning hybrids can often never amber, i had a Headband called Thelma. She was a weirdo twin seed. Her sister Louise actually turned out to be a kind of, Louis and ended up showing some balls. It was 2009s version of an LGBTQ plant. 12 weeks and you would see no sign of Amber. But after a souring high she couch locked you good and proper.