“the paint tool will open the Materials dialog, where now you can visually preview materials and access material properties in order to modify a material. You can see your changes without closing the Materials dialog.
Also, you can use the “Remove Paint” tool to remove a material that has been applied to a face.
Meanwhile, you can identify the quantities of materials used as Paint in material takeoffs.
EDIT In Revit 2012 and newer, the quickest way to identify paint is to use the Remove Paint tool. This does not load the Material selection panel, and will thus be faster. Also, switch 3D view to wireframe with Remove Paint to globally scan the project with your cursor for painted surfaces…