The colour of the ABV at the end of a session doesn't really tell the whole story. I think taste, desired effects, and vapour production should be the key factors as to when the load is ready for the ABV container. I find that I have to experiment with the strain to find the "Sweet spot" in the temperature, draw method, grind, loading, etc. Once the flavour drops off and vapour production is also dropping off I'll dump the bowl. I find that my throat is less sore and I cough less if I don't crisp the weed until it looks like dark brown coffee.
I just got some OG Kush that is vaping really nicely in my Herbalizer at 390F with some super tasty clouds, yet tastes like ass at 430F. I get a really nice cerebral high with a bit of a body stone at this temp which is exactly what I'm looking for in this strain. In contrast to the OG kush I have some Bubba Kush and Green Crack that really thrive at 430F and is still remain super tasty and their effects are improved. They come out darker and the flavour degrades faster but the clouds are more dense/potent, which I'm more than fine with though the session is a bit shorter than I would like.
I guess what I'm trying to say is that it's sometimes not worth vaping every strain until it's totally dark IME.