So I am assuming that you are using the Tranquility Tempate as it is the one that i first had a notion to try to change the background behind the logo. Is this the template you started with?
If not, let me know the link to your site.
If so, this is how you change the background using CSS:
Step One: Drag a <> Code Module into the footer of the page
Step Two: Add the following block of code into that module, changing the #hex colors to your preference
Step Three: If you want this to be the same for all pages on the site, click DESIGN> FOOTER> scroll to bottom and click SAVE FOR ALL PAGES
Here is a link to one Bookmark site that I have done this with Rosebud Continuum
Bonus tip: If you want the behind the navbar background to match the information popup, simply add the other CSS selectors as so:
Good Luck... let me know how it turns out.