Just before serving, tear--don't cut--the greens into bite-size pieces. Cutting greens with a knife will turn the edges brown with time.
Cheese can be frozen for longer storage time. Because the freezing process changes the cheese's texture slightly, it is best to use it in cooking or baking. (It makes it crumble when you try to shred it, but I deal with it and use it for all things anyway. The taste is still the same.)