Twitter is one such great service which allows you to express your thoughts very easily, just like other social network you have a profile page on twitter as well which you can further tweak to personalize as per your personality.
Here is how you can do this
1. Go to twitter.com and login in with your username and password
2. Now click the settings link shown at the top right of the browser screen
3. Now click Design as shown in the image below
4. As shown in the image above, you change the background image or change the design colors in shown in the background of the profile page.