When I go into the Swatches palette, and assign a new color, the column area (the area predefined as my column width in the Site Properties box) of my web page fills in with the newly created color! Nothing is selected on the page, and there are no rectangles or containers in the area that fills with the new color.
It is repeatable. I can close out of Muse, start a new site, and still have the same problem.
(Mac OSX Mavericks, MacBook Pro)