Hmm. So...the lightsource is coming from the west and the north/south faces have the same shading? Interesting. I'll swap out that cyan for a black and add your version to post #89.
Well... yes. Just realized you wanted the light to come from the southwest. To be honest I just swapped the cyan with that grey because of the contrast, that middle grey serves as the shaded part contrasting with the white and as the lighter part contrasting with the darker grey, so reducing color count (since it seems that matters to you) by one. I liked your stylistic choice of cyan though (that's why I used it in the center of the walls.)
Just thought that, as per the comments, people seems to have a problem reading the perspective. To keep the light source in the southwest you can either use another (darker) shade of grey or another (a bit lighter) cyan. Or do what you did in #2 and use the same darker grey for the north and east walls... Or just ignore me completely since you already know what you're doing
Aaaand I'll stop messing with your set, I promise