Converting .ai to pdf is changing colour of font

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Hi all, 

I am creating a plan in illustrator and when saving the doc as a PDF it is changing the font colour from black to blue. I am using the same page for two different layers, and one layer saves to PDF perfect (stays black) and when I turn that layer off and turn the other on (same colour, same format) it is changing my font to blue when I save as PDF. 

Please help!! 

Thanks 

[Monika Gause]

Please show the layers panel and tell us how exactly the PDF export is set up.

Also: do you view the PDF in Acrobat? If not, do that first.

[Ton Frederiks]

If Acrobat, is something like Preferences > Accessibility > Documents Colors Options > Replace Documents Colors checked?