Have you tried maybe rewashing the fabric?
I have never had fabric turn yellow on me but....I only store my fabric in air tight containers and even then I cross my fingers and pray. I once read that Silverfish (a little bug) loves to eat on fabrics that have been starched and pressed then stored!
I hope the starch did not discolor all your fabric.
I bought Kona Cotton SNOW WHITE fabric (three yards) the other day, got it home and it almost looks like a cream, but then when I cut the blocks the size I need them and they are away from the yardage, it turns to white again! How crazy!