Dynamic shape with solid fill does not plot solid black

We produce photomasks by changing the colors of the desired features to black and using the Plot command. This works well for most of the etch but not for dynamic shapes with solid fills, which print gray instead of black. Connect lines and cross-hatched fills print black but a solid fill does not. The gray is very dark and looks like black in Plot Preview on the screen but emerges distinctly gray from a laserprinter. The darkness varies between printers. Printing to pdf with Distiller gives a shape that looks black on screen but again becomes gray from a printer.

Can anybody suggest how to make the fill genuinely black, please? I am using OrCAD 16.3 on Windows XP.