My understanding is that it's the yellow component of the yellow-green stain that acts like a low contrast filter for variable contast paper. And, in the 3rd printing of Gordon's book, he goes into great detail about keeping the developing process entirely alkaline (developer and fixer) or neutral (water stop and wash). He recommends the Formulary's TF-4 alkaline fixer for maximum stain.(posted 8893 days ago)