[Renate]

The brute force way is to edit framework-res.apk
But that requires resigning your whole system.
You should be able to load a theme, but I've never done that.
Probably the easiest would be to mod your launcher to use a background.
You don't want your wallpaper to pan, do you?

I tried fine-tuning my Wallpaper.apk. It works fine on my phone, but not on my Poke3.

I don't know.

I just checked /data/system/users/0/wallpaper after I changed it to black.
It's a nice 1448 x 1448 PNG file of black.
So the problem is that the SystemUI never tries to draw it.