That yellow is a combination of the dye in the food and bile and it is a b**ch to get out! Ask me how I know. I had this happen on a completed quilt top (not quilted yet). I know you won't want to hear this but I never was able to get the stain out. I did however fade the stain considerably. I even took a chance and machine washed the unquilted top hoping to get it out. No luck. I quilted the top anyway (for practice when I first got my LA) and have yet to put the binding on it. I will try scrubbing it with oxiclean and all the usual suspects but I am not holding out much hope to get all of the stain out. You can try scrubbing and stain removers and such but you may have to resign yourself to either remaking the blocks or ripping and resewing the stained parts, or live with the stain.