[Scribus] Blue or Purple?

[Ciro Soto]

I have a basic question (and I disclaim my novice status as well)

I created my first book cover with Scribus1.3.0. and exported it to pdf.
I went to a printing store (Kinkos in US) and my beautiful blue cover
looks purple!!  The person in the store told me they use CMYK printers
and that it could be the problem.

So... how do I make Scribus create  CMYK colors in the exported pdf file?

thank you
Ciro