Filling Desktop (preferably with default desktop image or color)

I am making a login program with an option to clear the station's desktop to
make the interface cleaner for machines that only use my application.  I'd
like to clear the desktop to the options set for the station such as
background image and color.

I would assume, since Windows already does it, that there is a simple
function that will do this before the desktop icons and start menu bar are
displayed.

Any help would be appreciated!  Thanks.