Default Need Help in Wallpaper Changing

Hello
I have a Nexus 4 and using multirom with miui as primary and UT as secondary.
Everything is fine but I am not able to change the main homescreen wallpaper.
Its just white background and I dont really like it, too bright at night.
In settings, I have already selected same wallpaper for lockscreen and homescreen still homescreen has the white wallpaper. I really like that default ubuntu wallpaper and please tell me how to apply it back.