Since OpenOffice [1] moved to LibreOffice [2], direct consequence of Sun Microsystems bought by Oracle [3], some differences may have been felt, except name change.
One of them, on my LibreOffice version (actually 3.3.3), had a particular impact on me : my PDF exports were systematically black and white.
Fig 1 : Libre Office Writer colored source documentFig 2 : LibreOffice PDF export parametersFig 3 : LibreOffice black and white PDF export
A simple solution that I propose you, is to look in your print options (Ctrl + P). Once in the print screen, go in the LibreOffice Writer tab, and uncheck “Print text in black” option (Fig 4). Cancel is enough, it is not necessary to start printing.