Until recently, creating your own Chrome theme meant you either had to know some code, or you had to rely on a Web app. Google recently released a Chrome app called My Chrome Theme, that makes creating and sharing themes extremely easy and a lot of fun.
The app breaks down the theme creation process into three steps:

1. Import your image: Upload an image or take a photo with your webcam.
2. Add some color: Select colors for the toolbar, background, background tab, and frame.
3. Install & share: Install the new theme and share the unique URL with others.

The next time you launch My Chrome Theme, thumbnails for your themes will appear in a list at the bottom of your browser. Clicking on them will allow you to install, delete, or share them.
That's it. Keep in mind that the size limit for photos is 5MB and that you should only upload photos you have rights to use. Images from completed themes are stored on Google's servers.