I suspect 'coloring the two extremes' involves something more like 'wiring the luminance signal up to the chroma'. Again, try not to think digital. This isn't photoshop, this is signal processing.
Once you have a mostly Black, and White (with no greys) image - it's relatively simple via basic electronics to colour replace those with alternate colours - much like the old analogue chromakey 'blue-screen' techniques.