Hit escape or the great button to bring up your menu, then select Log Out. When it gives you the log out or view credits screen, hit escape again. Haze gone
Usually that only shows up if you change some UI settings, such as changing UI colour or something else under the interface options. It shouldnt be there any other time.
It shouldnt remain after you restart the game or return to the character screen anyway.
I think the haze that is mentioned is a blue-ish tint over all of your buffs. It is harmless, and yes, is cleared if you hit escape. It also clears if you get buffed again.