Initially, I believed the outline system wouldn’t have impacted multi-team gamemodes, as all enemies would just be simply highlighted in your preferred enemy colors. Unfortunately, glitching into the custom games menu, and using the options to swap teams, it seems there’s only a limitation of 2 max teams available: Cobra and Eagle, with an observer option. As shown here: https://i.imgur.com/2O1qbOf.png
There were not any options to increase the amount of teams, and that disappoints me so for the future potential of custom games. I can name a few very fun ones, from Multi-Team Castle Wars from Reach/5, Rocket Race H3/4/5/Reach, or Drag Race from Halo 5.
I surely hope this isn’t overlooked, and perhaps even have additions to adjust your outlines on a per team basis. I certainly hope that the outline system caused the lack of Multi-Team.