You can design your own skin and give it a background, choose your text and link colours and fonts, change the look of your tables and buttons. If you know CSS, you can also add your own custom CSS for more flexibility.
Go through the various options on the screen and make changes. You can then easily apply the skin that you created to a page to check it out.
If you want to share your skin, choose to make it public under "Skin access". Then others can apply your skin to their pages as well.