You can use Split Face on any non-family instance. The Split Face tool splits the selected face of the element; it does not change the structure of the element. After splitting the face, you can use the Paint tool to apply a different material to this section of face. See Applying a Material to the Face of an Element.
In the conceptual massing environment, a surface can host subregions that have their own properties. Creating subregions can help you refine your design and improve the accuracy of an energy analysis. You can assign a material to a subregion or extrude its profile into a solid or void form to change the topography of the surface.
A wall with a split face (around the window) before painting
A wall with a split face (around the window) after painting
To split a face
Projection type examples
Top down is useful for drawing skylights.
Parallel to level is useful for drawing windows.
In the following example, the wall around the window is split, so that it can be painted to match the border around the door.