I have mapped each color to a particular square in the 3×3 grid. So (in my coding):
black is represented by the bottom left square
dark gray is represented by the left square
light gray is represented by the top left square
green is represented by the bottom square
…
This coding and decoding takes some mental effort initially. But after some time the brain proceeds automatically. Then, Stage 4 (colors) feels equivalent to Stage 3.
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