Me & Jason went through a problem with white a few weeks ago. It'd pour bright white for 3-4 craws then itd go south & start turning yellow. We did some experimenting & as soon as we put the plastisol in the cup (filled to 3/4cup) I added 40 drops along with my white & stirred it in before we even did anything.After it was heated each time we re-heated i added 10 drops & stirred it in & it stayed bright white the whole batch.you don't have to add that much to the other colors,so colors like your black grape & blue ect I'd add 10 drops to keep it where you want it