Hello PJ Melies,
With Q3 2009 we have introduced an improved rendering of the Dock control that solves number of problems reported by customers (RoudnedCorners for example). That is why these table-cells contain images. If you apply background-color to the respective table cells, the color will not be seen, because of the images.
To make the "border" around the dock have the same color you should modify the image sprites so that they have the desired color. Here is a
link to a help article explaining how this can be done.
If you don't plan to use rounded corners you might as well hide (display: none) the table cells shown in the project below.
Sincerely yours,
Pero
the Telerik team