What is the purple hue around enemy armies in Total War: Warhammer?

Sometimes when I defeat an enemy army, the campaign map shows a purple aura around the defeated army. What does it mean? I don't recognize it from previous Total War games.

It should be noted that I am playing with the Wood Elves DLC, as well as some mods. The most sizeable one being Radious' overhaul of the game.

Solution 1:

That purple hue is just a cosmetic thing that happen when you won a battle. This happen to me only with Chaos (playing with him and won versus Kislev and killing Sarthorael with Chaos too), Bordeleaux (just autoresolve the battle versus Red Horns) and also with Clan Angrund (versus Greenskin).

Also, when you won a battle versus Sarthorael, no matter if you are Chaos or another faction, in the campaign map, littles purple tentacles appear.

There are different cosmetic things on the campaign map.