For problems with backlit (in my Xperia P backlit of transperent bar stayed on after making or receiving a call, i had to reboot my phone to fix it, every time this bug showed) i recommend to flash framework by @jatinrungta
AFTER installing this pack.
It seems that framework provided in this pack is some kind of broken (i had some checkbox glitches and this bug with backlit)
Now everything seems to be ok, but widgets not follow theme color, and some ui elements (switches etc.) doesn't change when applying some of new themes (like "Tri-Flat" for example) - probably this feature was overwriten by flashing jatinrungta framework. I don't know for sure. Someone with better knowledge could look into it.
But... i don't have hope for it cause best modders/devs moved to newer devices and they're not updating their mods for P,U,etc. anymore
Maybe it's time to change this awesome device for something newer too
PS. This post is not meant offensive in any way