yes I agree with you but then there is only what I drew in white lines that come out black when printed... All other colors come out with grayscale! And the worst is the yellow, you really can't see much of it. And I have the same problems when I print in pdf.
If it can help, under autocad, the print management is well done, on the other hand under Draftsight it's a hassle. First, take the "monochrome" style and check that for each color "Print style" the line color: " is "black" FYI, the "couleur_7" is black when the screen is white and white when the screen is black. At the same time, check that the thickness of each line is at least 0.3mm because above for some laser printers that are not too precise, it will turn gray, or even almost disappear.
Finally, avoid RGB colors, you must stay in the basic Autocad colors because it is not possible to configure them.
To make a PDF export, use a "virtual PDF printer" of the PDF creator type, making sure to configure this software with a minimum of 600dpi to prevent it from converting everything to gray and use the same settings as for an impressive laser: Monochrome.