The iMovie video effect "False Color" (found in Quartz Composer) recreates your video clip in two colors of your choosing.
iMovie Video Effects - False Color
Effect In, Effect Out:To apply the effect to only part of the video clip, move the sliders to the places/times when you want the effect to begin and end. Leave them both set to 0:00 to apply the effect to the entire clip.
Color 1, Color 2: Click on these buttons to choose the two colors you want in your video clip.