OsnapzBG is a background color changer app that now also supports AutoCAD 2013 and is now also available as AutoCAD app on Autodesk Exchange Apps site making installation easy and having it show up on the Ribbon Plug-ins tab. This also gives quick access to easily set OSNAPZ on or off.
OSNAPZ set to 1 (on) makes anything you snap to only use the current elevation as z value. OSNAPZ controls whether object snaps are automatically projected onto a plane parallel to the XY plane of the current UCS at the current elevation.
Download available here.