This is a good ideea indeed -- I was about to submit this myself <img border="0" title="" alt="[Smile]" src="images/icons/smile.gif" /> .
I did a quick hack on 4.1 to implement this, but some changes are needed in order to do this right. To print black text on white background the function that sends the page headers should be modified to send other values for text and background. My modification did not alter this; it removed some of the graphics headers and the blue backgrounds of the post tables. This way you can use "black text" to get black text when printing from netscape.
The modification is simple: the displaypost.pl checks for the variable print before printing the headers. If it's 1 the headers are not printed (I chose the flatmode side-headers for printing) and another routine that doesn't print the backgrounds is triggered. It is important that _no_ backgrounds are defined, otherwise netscape will be confused by the multiple backgrounds. You can check out this (and the other modifications) at
http://forum.gameover.ro (the printing option is the last icon (the one that looks like the edit button) in the navbar.
Scream, let me know if I can be of assistance.