Fairly self-explanatory. I roughly understand why this hasn't been done yet, but I think the GoodLock devs could figure out a workaround.
In short, there's a reason why not a single other phone manufacturer styles the icons on the app screen and only does on the home screen. With the home screen, you can control which apps you put there, and you can deliberately only use themed icons there. The app screen, however, lists all of them, and half the apps don't support coloured icons. Mixing themed and unthemed icons together looks horrendous and discourages people from using themed icons at all (which, let's be fair, aren't that good to begin with).
We really need a Home Up feature to disable icon theming on the app screen, while keeping it on on the main screen.