First off, not all novels need a theme.
As a matter of fact if a theme doesn't naturally bubble up from your subconscious, you probably don't want to try and wedge one in there just because it sounded cool to have a theme.
We have all read those books where the author thought the color chartreuse was awesome and found some way (usually not a very pleasant way) to interject it freaking everywhere.
Join me on Saturday at 2pm PST to discuss how to get your theme on without, you know, annoying your reader in the process