I figure the one just sat around for longer, as I've had extra blue-y cheese develop in my own fridge. Just never seen such a striking difference at the store, which I found mildly interesting.
Actually I do see bad mold, but it's all over the other cheese, it's super hairy and white so it's hard to tell, but yeah, I can tell, that lighter one is no good! Seriously, you'll die if you even smell it, I can see it! I've eaten so much cheese