I think he's saying that he wants an alpha-blending mode that moves by ramp steps rather than just by value. In his greyscale sprite, I think he used an alphablending tool to go up the gradient from one color to the next. Ideally, he'd like to be able to draw the silhouette in the base, darkest color, and have the alphablending tool have each progressive "layer of paint" go to the next step in the ramp.
I may be completely off, but that's what I got out of it, and it sounds like a potentially cool idea.