Can U supress color when encoding black & white source w/DivX?

I encode some old black and white films sometimes. DivX does a generally very good job but creates some false "clouds" of color. Not intense color but enough to be anoying. Is there any way to "turn off" or filter the color info out so the encoded file is truely black and white? I'm not a veteran encoder so if the answer is obvious please don't slam me.
(edited for uh... typo)

 

xvid, there is grayscale encoding.

 

Thanks shiroh, perhaps I'll give XviD a try.