

Null would be completely blind, no visual data at all. Monochromacy is receiving a single visual channel instead of the more common r,g,b. The original Nosferatu had more colour than that and very few people would argue that’s not a black and white movie.
0 to 1 is monochromacy, a single visual channel, eg only rods and no cones. I thought that was fairly clear. Full colour vision would be closer to 0,0,0 to 1,1,1 (plus low-light rods). Null would be no visual channels at all, ie completely blind. I didn’t miss the point of your example, it’s just a very bad analogy.
Here’s a quick article I found which demonstrates how individual channels are monochromatic and you only get full colour by combining channels, digital image formats were designed for human eyes so this is much more analogous to human vision. With no channels you get nothing at all.