We have been thinking about this a few times in early development.
At some point I even added a syscall, allowing the the cgame module to replace the colorTable, but we decided not to keep that in. We don't want everyone to see different colors.
As for adding grey and orange, we realised that due to 1.02 and 1.04 escaping ColorCodes differently the players in 1.02 and 1.04 have developed different behaviour regarding the use of colorcodes. In 1.04 using "^a" for red is quite uncommon, because people still see "^a" in the console instead of red. In 1.02 "^a" is escaped the same way as "^1" so people don't see a difference and they use whatever they feel like using.
If we would start adding more colors "^8", "^i", ... won't be red for people using JK2MV in 1.02. All the colors higher than "^7" and "^h" would change (cause the colors are like a "circle" and you increase the amount of colors in the "circle"). BaseJK users and JK2MV users would see different colors in names, chat, etc. And we want to avoid that.