Why think that the colors are a torch job?
What looks odd to me is the fit of the barrels to the breech. It is possible that the barrels are replacements that were made in Belgium.
If we consider the condition of the German and Belgian gun industry just after WW1, we can see that a small shop may have put this gun together from what was available.
I agree that this is at least $1000 out of reality.
Best,
John

Humble member of the League of Extraodinary Gentlemen (LEG). Joined 14 March, 2006. Member #1.