By The app on the or rather the settings availble in XZ basically only increases the brightness along with the back light , therefoer loosing the clarity and rich colors when in maximum ,
Here is an app which can controll it individually , indoors i like the setting 50 % on both levels to get that dark deep colors along with minimal brightness
https://play.google.com/store/apps/details?id=mobi.omegacentauri.ScreenDim.Full&hl=en
test ur settings and post your likings and settings config below is something intresting , the samples with the viewing angles after I have set the app to 50 - 50
Before the app with 100 % brightness check the head on screen and the side view
Samples. On xda link http://forum.xda-developers.com/showthread.php?p=43769528
and then after the app enable with 50% setting and additional deep viewing angle
Edit 1 i can 100% confirm viewing angles are great than ever with 50% on both... and derpest colors.. love xz more than ever...