Google tells me my fonts are too small - I'm using a copy of the Default theme, light colors.
I went to light.css and changed a couple 85% font-sizes to 90% and one 11point size to 12. That's all I did but now my background color is white.
I tried uploading my backup copy of light.css and got back the background of the thumbs, but not the background of the page.
your theme instructions say:
"pick the theme color by going to the Admin Options tab and changing the Theme colors option."
- but there is no Admin Options tab.
I did this before but now there are no choices besides the four dark-light-etc.
Where do I go to fix font size and background color? The common.css says 100% for font size, so that's not useful.
http://thewinawards.com/gallery/ 
Zenphoto
Comments
Since you're using a copy of the basic theme, make sure you have no conflicting theme options.
(http://www.zenphoto.org/news/theming-tutorial#themeoptionsphp)
You also have a "Fatal error" on your pages:
Call to undefined function printFavoritesURL()
I suggest you try to fix that first.
The theme uses relative font sizes. You have to adjust them in the specific css file of the one of the four theme personalities you are using.
Or where you saw this error.
I just want the background color to return.
As I said I only changed the font sizes on light.css
Followup:
I fixed it by using a different theme - "default" wouldn't let me duplicate so I used "basic" and made a copy and started over.
I'm going to leave the fonts the way they are and search for a better theme, I guess.
The problem of font sizes is still not repaired and why I couldn't just change font sizes in light.css.
Regaring the font sizes, they are relative and therefore the cascade in Cascading StyleSheets kicks in.