Ok, maybe I had a different interpretation of the scenario OP presented. I read the "solid block of average color" as simply an average of 2 colors, not a weig

Ok, maybe I had a different interpretation of the scenario OP presented. I read the "solid block of average color" as simply an average of 2 colors, not a weighted average. So black text on white background would always result in rgb(128,128,128) (#808080) regardless of how many pixels of each color you had in the block. The only things that leaks are the color of the background and of the text but these are already known from the surrounding parts. This makes sense for purely aesthetic reasons because the pixelized block will not stand out against the combination of background + text around it. A white page with black text would have a gray fuzzy area where it's pixelized. If a weighted average is used and you can determine the fill factor of the text inside the box that would be some information leakage, as small as it may be.