bro, just tell him to add some more GBL, not vinegar, you have to add LOTS of vinegar, just tell him to drop more and more GBL in till it neutralizes. About the yellow tint, was the GBL yellow to begin with, i know IP sold some yellow tinted shit, they NaOH may have NOT been USP grade either, if not i wouldn't drink it, because there's a lot of impurities in the GBL and the NaOH if its not the highest grade.