That should be your weightmap, and the color determines the effect it has (green is none to least, through the spectrum to red, which is the most effect).

I was assuming green was total effect and red was falloff. The head, after all, is moved 100% by the head bone while the neck tapers off.

In the old days, the falloff spheres were red and green, with the effect of green being 100% and red falling off to zero. These days I guess it falls off of the rainbow.

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