You can change the background of your blog at any time, to make it more personal. There are solid colors, photos and even some videos you can use. To change the background, go to Backgrounds under the Blog & Network menu. You can see all the available options there. Simply click one of them to change the background and it will automatically update.

Related articles:

Creating a blog post
Adding an image to your blog post
Blog activity feed
Network friends and contacts
Network interests and location
RSS feed
Promoting your blog