The yellow contaminants you want to leave out (dmt-n-oxide) are fine and equally psychoactive. But if you really want them out, aye, put the yellow spice in some container, add warm naphtha to dissolve it, soon you'll see yellow droplets of the "contaminant oxide" falling and gathering on the bottom of the container (will look like yellow/orangy/red syrup). Just get it out (e.g. siphoning it off?) and freeze precip the naphtha for whiter product