Thanks Dragonfly,
I think the problem might be somewhere in Scribus pdf export settings. Everything in the Scribus files in C=0, Y=0, M=0, K=100. But when I export to PDF and select a black line (in Foxit PhantomPDF) it's showing:
Hue: 14
Sat: 19
Lum: 20
Red: 22
Green: 20
Blue: 19