Custom Clock Icon gives Winterboard themes the ability to modify the clock icon appearance. Fully integrated with WinterBoard, just enable a theme that supports Custom Clock Icon in WinterBoard, do a respring and everything should be working.
This tweak is open source, source code and a detailed description for themers is available at Github
No options to configure for the end-user; the appearance is configured by theme-makers modifying theme's info.plist file.