Developer website: cf/x
b/w plus one is an iMovie plug-in that will make a color clip grayscale -- plus one additional color. you select the color (and leeway), and all other colors will be converted to grayscale. it works best with clips that have one color that is stands out, but since our plugs support are of effect, it also works well with more complicated clips.
Mac OS X 10.2 or later, iMovie 3.0 or later