Yeah, complimentary colors (inverse) can appear grey if you dither them 50/50.
So: What constitutes a color(s) as neutralizers? And does having "neutralizers" or greys add to the challenge?
"you cannot use any grey"..
pixel-advocates know ask themselves whether a 192-192-193 is still tolerated or not. any defined range for your 'neutralizers'?
-Working on my last second entry-