First thing is, we need to properly identify what an amber trichome really is.
I truly feel the amber trichome is very mis-understood.
A true amber trichome will not be withered, it should remain clear or translucent.
I truly feel a withered tricome has gone too long, it is over ripe.
But
We need to test this idea with real science.
Me personally, I use sex organ maturity to judge ripeness.
You can find more on amber trichomes here.