[SOLVED] Fixed grey background in MENU 1

Atahualpa v. 3.5.3 -- WP v. 3.0

I've set the "Background Color" in ATO>MENU 1 (Page Menu) to FFFFFF. (In fact all my settings on that page are FFFFFF and 000000.) The menu items all look correct. However, the unused portion on the right side of the screen is grey (looks like DDDDDD).

Is this a bug with 3.0, or (much more likely) am I doing something wrong? Any ideas on how I can fix it? I'm using the Theme Tester plugin, so providing a link to my site would be useless.

Thanks in advance!