One of the nice features of touch-based Windows Mobile 6.5 devices (unlike, say, with the iPhone) is that you can really customize the user interface, with a color scheme, menu and balloon window styles, and custom (photo) wallpaper that is visible under the top-level UIs, not just at the welcome screen. Now, Microsoft lets you create your own Windows Mobile 6.5 theme, using the web-based Windows Phone Custom Theme Creator:
Want to set your phone apart from the crowd? Make your Windows phone* an extension of your personal style by designing a custom look for it. Use your favorite photo or any other image, add colors and style, and then text the custom theme straight to your phone (or your friend's phone, for that matter).
*The Custom Theme Creator works with Windows Mobile 6.5 touch-screen phones. (Click here for instructions on how to tell what version phone you have.)
Thanks to Patrick H. for the tip.