Download and learn more: https://developer.sony.com/themecreator
With the free Theme Creator BETA you can customize over 300 graphical assets like icons and buttons to create your own professional-looking theme for Xperia devices. The tool is intended for designers, and built to let you focus fully on the design. When you’re ready to export your theme, one click is all that’s needed to create an APK file that can be installed on an Xperia device.
Getting Started: https://developer.sony.com/develop/smartphones-and-tablets/theme-creator/get-started/
Requires Java Runtime Environment (Java Download page)
Theme Creator BETA tool: https://developer.sony.com/downloads/tool/theme-creator/
Approximately 118 MB, Agree to EULA to Download 'theme-creator-v0_0_1-beta.jar'