Nik,
I think two steps are needed in order to make this a historical, or at least less ahistorical, mod.
First is easy - leave the trousers unmodded. Heer soldiers wore camouflage trousers only as part of the winter reversible camo suit with parka and a pair of trousers (or if they themselves comissioned the trousers from some tailor - effectively a real-llife uniform mod). The winter combination would be too warm for Italy or Normandy.
Second part is more difficult - you would need to somehow try and paint over the buttons, pockets and the belt. I do not know enough about modding, alpha channels etc. to tell if there is any way to do it and have the mod look halfway decent, but the real life camo jacket had none of those, one would wear the feldbluse and the webbing underneath it. Here the only exception would be private purchases where an officer or NCO would pay a tailor to produce a feldbluse equivalent usually from a camo tent material (the picture you show above is either such private purchase or a re-enactor's kit itself historically not accurate).
All the best,
Zwolo