[Scribus] white turns into black after exporting to pdf

[Peter Lesterhuis]

Hi,
Newbie question: I just created my first brochure with Scribus. It looks 
fine on the monitor. I saved the document as pdf. When I view the 
document in Acrobat Reader it turns out that all white fields are 
changed into black. So now I have black text in a black background.
I played with different settings, read tutorials about lcms and 
icc-profiles. I know a lot more about colour management now, but the 
background is still black.
I sure it must have to do with settings, but I can't find out which and how.
I would appreciate if anybody could help me.
Peter