I noticed while checking my site on my friends mac that the main navigation background on top of the header, the one with the home and Log In links does not show correctly. To be more specific, the background color does not show as instructed in my stylesheet. It should be green, but shows white or transparent I guess. I wonder why this is? It is only doing this on a Mac. Ie and FireFox on a pc are showing correctly.

Here is what I have in my stylesheet.css:

#navMainWrapper, #navSuppWrapper, #navCatTabsWrapper {
margin: 0em;
background-color: #006633;

On a Mac it shows like I would put background-color:#000000;

Is there a tag that can be added that would fix my problem?