Well its kinda complicated because when you're extracting spice, you're pulling other stuff together. The rate at which each component (like, say, DMT, NMT, DMT n-oxide, plant oils, etc) is dissolved depends on factors such as heat, time, surface area/mixing thoroughness, etc. Also depending on how much of other components are present, things can be more or less easily dissolved in a solvent.
I say this because there must be some kind of optimum temperature/time of mixing to get most alkaloids with least other impurities, but so far nobody made so extensive tests and analysed afterwards to tell for sure.
What we do know from experience is that a solvent does not need to be yellow to be full of DMT. DMT is not yellow, neither is NMT, so yellow is more likely plant oils. It could be that both come together, because the longer you leave, the more DMT/NMT also are dissolved, so some people have equated yellow with alkaloids, but it might be that it proportionately increases more the amount of oils to alkaloids if you wait for too long.
Also notice it has been documented that while dmt n-oxide is not soluble in naphtha, it IS soluble in naphtha that has oils in it. So in the case there might be some n-oxide in your spice, if you want it, having plant oils and leaving for longer might be good.. But then again, there is no direct evidence yet, AFAIK that n-oxide is present in mimosa or created in significant amounts during extraction conditions, so maybe DMT/NMT is all you want.
And by the way, no worries if your spice is yellow, just recrystallize it if you want.
Oh and, here's one relevant thread:
https://www.dmt-nexus.me...aspx?g=posts&t=11715