When printing to a color printer, lines are drawn using black and white (color count 2). PDF output is rendered correctly. Color printers and Microsoft virtual printing (XPS format) show the line item as black and white.

This code reproduces the problem:

QPrinter printer;

QPainter painter(&printer);

painter.setPen(Qt::magenta);
painter.drawLine(79 ,112 ,711, 160);

QBrush brush(Qt::magenta);
painter.setBrush(brush);
painter.drawRect(100,100,100,100);

The output will consist of a magenta rectangle, with a sloping line that's drawn in black and white.