I did hard-reset my FP today, restored all apps from the standard “Backup and Restore” app, and re-activated the XPosed framework and GravityBox. Needless to say I lost all my settings. Highly annoying.
Yet, this explains a thing (but not two): the Ultimaten notification control is now available for 19 reboots. I can access the notification settings and led control for any app now. Explains how I changed the colours in the first place. Does not explain why the colour changes I do now are not set in practice.
So, quite probably I was mistaken, and did not pay 2.90€ in the first place. (I will, in the near future. I like the feature, and want to support the development of GravityBox.) A slight doubt stays, since I experience some strange effects of the wipe-and-restore stuff.