Hello,
Most printers (virtually all consumer printers) cannot print white on black paper, inherently due to their design.
The technical explanation for this is that white is represented by using no ink at all. The intention is that white paper will be printed on.
One possible solution to this is to invert an image of white text on a black background, and print it on white paper (the printer would effectively print black ink 'around' the white letters - white due to the white paper which has not been printed on). However, this will use a lot of black ink, especially with large designs, and may produce a poor quality publication.
Another possible solution is use silkscreen printing. However, the solution will depend on what it is you're producing...
You may have to abandon the idea of printing white on black.