It looks like the tcx framebuffer is capable of supporting 24 bit
      color, but a tcx framebuffer under netbsd will only support 8 bit
      color.  (This seems to be true in 1.4, anyway.)

      Is the tcx framebuffer likely to be supported better anytime soon if I
      don't find time to write the relavent code?  What code does need to be
      written to make it work?

   the tcx driver is, as i recall, very basic -- just enough to work,
   but none of the smarts available through the hardware.  i'm not aware
   of anyone working on it so anything you do to make it better would be
   excellent!

Do you have useful documentation?  I can't promise that I'm going to
have the time to do anything about it soon, but I'm at least curious
to get some idea how much work is involved...