No matter what color you try to use, this isn't going to work very well.
Most printers can't exactly line up the characters on two passes of the same
paper, so you're going to get fringes or shadows. If you use an inkjet
printer, it gets even worse because the paper expands and shrinks a little
bit as the ink wets it and then dries.

Why can't you just print the document once with black ink?