Dim3nsioneer, thanks for your response!
How should one know which settings defined in Cura are and which are not taken over by UM2 and is this documented somewhere?
When Cura is set to generate Ultigcode for UM2 would it then not make sense to have settings that are to be defined on UM2 itself greyed out in Cura?
There is a Cura documentation; the temperature thing is e.g. mentioned here: https://ultimaker.com/en/support/16586-basic
However, you're right about graying out (or leaving it away completely). This is still a bug of the Cura beta (I guess you're using V1.99?). But it's noted by the dev team.
Found the temperature mentioned via the link you provided.
Btw: I'm using Cura 15.06.03