pishposh, I think your idea comes close to what should be done.
We need to keep things simple.
00-15 should be legacy. These numbers are already mentioned in the
EGA Color Table.
Ignore the numbering scheme for the sixteen colours in the graphic.
16-63 should be the other 48 colours in the EGA colour table.
There is no need for redundancy in having the first 16 colours twice.
64-75 should be for shades of gray.
Since 000000 (black), 555555 (dark gray), AAAAAA (light gray), and FFFFFF (white) are already included in those 64 colours above, that leaves 12 shades of gray in 4-bit grayscale.
111111 ... 444444, 666666 ... 999999, BBBBBB ... EEEEEE
76-95 should be for local customizable colours.
Of course, some people may use them remotely, but oh well.
I do agree, 20 seems like a good number.
96-98 should be reserved, otherwise more local customizable colours.
99 should be for transparency.
