I have a new article about making isometric pixel art in Blender using compositing nodes. The dithering in original article snapped the three RGB values to 0 or 255 for 8 possible colors. My new method allows you to snap to any number of steps to simulate any color depth. For example, if you snap color to 5 steps you can approximate the 15-bit color depth of SNES. I also add outlines using compositing nodes and Freestyle. The whole node setup should be ready to make game assets with little modification.

https://bradeneliason.com/isometric-pixel-art-in-blender/