I pulled a print out of the tank. The background is cyan. The rest is perfect. Not close. Perfect. I'm the only one who would notice the off background. Should I accept the off background?
Could the old bleach be an issue? The developer and stop are fresh. If it was a chemical issue I'd expect a bigger screw up then just the wall. No?
For what it's worth IIRC the film is Agfa Optima on Kodak Supra.