You mention a lookup table would have been tedious, but surely an easier method.

This might be a case of "to a hammer everything looks like a nail".

The solution in my familiarity would be to align the emoji in a grid, take one screenshot and write a script to iterate over the pixel data to figure out the most dominant color and how dominant. So the build of the lookup set would be automatic.

Less interesting for sure but easier (at least for a JS dayjob skillset).

Similar to a below comment, I know this isn't the point. Thanks for an interesting write up