inDesign Preferences, Display Black setting is I guess different. One of your documents may have the display Black and Rich Black to show different on, check those (don't know what it is called in German but take a llook at the preferences and try to find it)
Check Edit > Asiign profiles. Do the documents both have the same colour spaces?
Check View > Overprint preview and View > Proof setup. Are they configured the same?
Check Window > Output > Flattener Preivew. Does one document have transparency and the other does not?
Check what Frans said.
There are a lot of things that decide how InDesign displays colours.
thank you for your reply, but that was not the problem
thanx, it was asiign profiles... coated FOGRA27 and coated FOGRA39 make a huge difference on blue
Ah, for some reason I thought I read 'black shows different' not 'colour', my bad, I read it the wrong way!