I shouldn't have any fox tails I've lowered the temp overall in the grow room in hopes of bringing out the natural purps if any in the strains it's stays about 75 lights on and down to 65 lights off.Strains that don't amber need to be judged by the look of the overall plant. Cloudy trichs yes, how swollen the calyx's are. Pistils recede, the frosty-ness will appear a little darker. Sometimes foxtailing will help you judge depending on the the strains characteristics.
I have heard that too about Gorilla Glue #4.What I meant was some strains will foxtail around the time they're finished. I have Bruce Banner and it foxtails right at end. I believe gg4 does too.