Why did my strudel/phyllo dough turn olive in color?

A couple of days ago, I prepared a phyllo pastry dough for an apple strudel. I couldn´t roll out the dough that day, so I left it in the fridge, inside a plastic bag. I recently looked at it, and its color is darker, almost olive. I can´t find anything that says that the dough should be used in less than 48 hours.