So your basically saying screw them all since it's impossible to include everyone? I just outlined for you the most common disability, it's particularly easy to avoid since they can still actually see.

> the rare person who is monochromatic can use the same solution as someone who is completely blind.

...how would you like to be told to learn brail in old age just cos your eyesight isn't quite good enough to read some small print?

No, that's just awful. Shape first, colour purely as an extra, then brail if the symbol is not relief or discernible enough, this is absolute basics of accessibility. This also helps everyone and functions in very low light since we all have low sensitivity to colour compared to luminescence, more so the older you get