I've noticed this with RubyMine 2.0 RM #91.15 on Windows XP SP2. Printer is Canon inkjet Pixma MP780.
If it's a bug, hope it makes it into 2.0.1.
Printing works fine when I print code in any TextMate-style scheme with black text background, such as Railscasts.
To save the ink I customized colors in Default black-on-white Color & Fonts scheme.
One change was to use orange foreground on black background for method name.
Method name, as the only black-background string, would be easy to find on paper.
But, the black background does not print in this mode.
The method name prints orange on white.
Please see screenshots below:
On paper "index" prints in orange on white, not orange on black.
I hope it helps you track this down.