Quote - At the end, given your assemblied linear color, c, you use:

s.Alternate_Diffuse = c * (HSV(c, 1, 0, 1) ** -.4)

Wacky, huh? 

The curve for this is very similar to a gamma correction curve.
From WolframAlpha :-
Above forumla -> Graph[x/x^0.4,{x,0,1}]
GC(2.2) -> Graph[x^(1/2.2),{x,0,1}]