At XDA developer forums, Dave has created a simple accent color changer application for Windows Phone 7 devices with help from Rustygrom. The application lets you edit the name and color value for all 10 of the installed accent colors in the normal WP7 device. You can edit the color through this application and then switch to the edited color in the Settings for the changes to take effect. Thereâ€™s also a way to reset the theme to default.
Source: Daveâ€™s blog