There have been other crosshair color features that use their way of changing colors. Doing in Hexadecimal, RGB,...
These are in OpenArena, Devotion and others.

But there's one that only existed at the year 2002 and the source wasn't never shown or has been completely lost.
This one has appeared on an old mod called Bid For Power.

I managed to dig this ancient feature and the source code is now here!

https://github.com/ec-/baseq3a/pull/28
https://github.com/LegendaryGuard/baseq ... c881bc237f

BFP commit (that's where I managed to get firstly):
https://github.com/LegendaryGuard/BFP/c ... 4be4acd278

INSTRUCTIONS TO ADD IN YOUR MOD OR SETUP (the instructions are the same like this link: https://github.com/ec-/baseq3a/pull/28, I do a backup version here just in case of lost info):

Keep in mind, the official Quake 3 gfx.shader, the crosshair is "broken". What that does is making the crosshair unable to be interacted with the colors. So, cg_crosshairHealth has never done nothing since this official shader has been staying there.

The modified gfx.shader is added in the repository and in pk3 package and the crosshair color can be interacted without problems.

If you've your own gfx.shader or your own shader, what you can do: You need to remove in gfx.shader the following lines that impede colorizing the crosshair, in this link you can see what should be removed, just click to toggle that arrow:
https://github.com/ec-/baseq3a/pull/28

cg_crosshairHealth must be disabled (0).
Just set 2, 3, ..., 6, 7 or 8 the color you want to set for the crosshair.

2: BLUE
3: GREEN
4: TEAL (CYAN)
5: RED
6: MAGENTA
7: YELLOW
8: WHITE

1: BLACK (That's special, in UI menu won't show and only shows as white - that isn't a bug, it's a feature and works exactly this way as worked in the mods from 99s and 2000s).

Screenshots about how it is in the interactive UI and how it is in-game: