color shifting foods

I have a tub of guacamole in my fridge; it's been sitting in there for a week. I haven't paid much attention to it, but I clearly remember that when I put it in there, it was bright green. Now it's turned into some odd shade of gray. I think that's an indication that I need to thow it out.

Sometimes I wish that everything would change to a different color so that I would know when to thow it out. Milk, for example, should do that (ever tried to drink milk that went bad? So nasty!). So should my bank statements. Right before I recently moved, I found bank statements that were 7 years old, and it was mixed in with all of my other more recent piles of documents. Oh well.