1st i had to find where the clocks are stored,
open LGAlarmClock.apk in 7zip, and navigate to res/raw-xxxhdpi
now pick your stock watchface background that you want to modify.
I chose the black one. And since I'm a Louis Hamilton fan, i chose to drop in the Mercedes Petronas F1 team.
after you replace the stock .PNG file with the modified file. Use ES File Explorer, or any other Rooted file browser that lets you set individual permissions. Drop LGAlarmClock.apk back in sysem/priv-app. Change the permissions for the .apk to from rw-rw-r, to rw-r-r, Reboot.
The Results: (sorry, had to use my ****ty S3 cam)