Monster name colors for simple UI improvement.
Other groups' guildleve, behest, etc... monsters should appear purple to you even if that group hasn't yet engaged them. As it stands, it looks like they should be able to be attacked (or possibly aggressive), but they aren't. This is something simple that would improve playability in crowded places.
Also, making the monster's name in the targeted window the same color as its hovering name. This will easily enable you to make sure you've targeted the red monster in a crowded pull.
This seems like it would be a simple change, and would improve playability in crowded areas.