In the Steam version of the Kingdoms expansion, various settlements will have buildings and walls that are chocolate colored on the battle map. There's seemingly no rhyme or reason to the coloration, but it's certainly not the intended color for the various buildings given the fact that they'll be right next to normally colored buildings. The game remains fully playable however, just looks a bit uglier.
In any case, I haven't found any explanation for the issue or any way to restore the buildings to their original color because I find it rather distracting. Seems to only be an issue on the Steam version of Kingdoms as far as I can tell.