Another thought that crossed my mind is why can't they produce a keycap like on the Selectric? They are engraved letters. Can't anyone make such a thing? The molds for the keycaps would have the letters "sunk-in" every cap. What does this mean? It just means that you can have keycaps that have no color whatsoever, but you can still see what each cap represents. Be it any color of the rainbow, it makes no difference.
However, you can always fill the gaps with any color (contrasting or not) you prefer.
Just like on the Selectric Blue.
Maybe old is new again?