If the broccoli in your fridge has turned yellow, it means it is past its prime. As broccoli starts to age and degrade, the bright green color will fade to yellow. Broccoli that has started to yellow doesn't necessarily mean it's rotten (unless you see mold/slime, in which case, it is!). But while you could technically eat yellow broccoli, it won't taste very good (likely bitter), so we usually recommend skipping it and starting with fresh, green broccoli.