I've used Patchouli EO lots in my soaps. Unfortunately, I can't answer your question on whether it discolors or not, because I always colored my patchouli soaps a rich brown. Patchouli has always struck me as a very brown scent. So I use ground cinnamon and cloves and nutmeg to color the bars, and call it "Patchouli Spice". The spice scent doesn't really come through, though. But I bet a spicy scent would go well with Patchouli. And Amber! I never tried it in soapmaking, but I have mixed amber oil and patchouli oil together for a perfume, and it was Ummmmmmm..... heavenly! Just some thoughts, don't know if they are useful or not. Good luck, Blue