ZDoom

ZDoom only has per-gamemode player settings, meaning that it's Doom, Heretic, Hexen, Strife and Chex. Both UrbanBrawl and Harmony identify as Doom so they both share the same setting.

I think to do this right a lot more work is needed. In any case, this is not a bug, more a missing feature.

Right, so this has nothing to do with colormaps.

To reproduce:

Load up any of the Doom games. Change the Player's Color to Brown for instance.

Then load up Urban Brawl. Attempt to change the Player's Color (it won't change from Custom, but do it for the sake of doing it).

Then load up any of the Doom games. You will see that the Player's Color is set to Custom.

Urban Brawl shares most of the Doom setting properties (as far as I can tell), so in the failed attempt to change Urban Brawl's settings, it manages to change the setting in Doom.

Huh?

Given that this is an IWAD, what is there to override from Doom? I don't really get what you mean here.

Anyway, the difference may be explained by the fact that UB's COLORMAP lump is put in the colormap namespace, rather than in the top-level namespace.

It probably should be treated as a different game (or treated differently in general). Harmony is not affected by this though, but it is worth some consideration.