Much easier is make all respawn points neutral. Then you change your gametype to, for example, team slayer, add respawn zones in a way that they surround certain amount of neutral respawn points, change team color of the respawn zone, and also change the "game specific" option to true. Then you'll have respawn zones active just in this specific gametype, in this case teams slayer. So when you choose in custom game lobby FFA you should spawn randomly on the respawn points, and when you choose team slayer, which has extra respawn zones added, you should MORE LIKELY spawn at the team side, for example. Respawn zones just increase the odds of spawning there, there's a topic somewhere, i guess, which explains it better, but adding respawn zones will make players spawn on the certain areas of the map, and it will also save you so much trouble with setting every respawn point to specific team color.
I hope it'll help. Of course i used the example of team slayer and FFA, but it will also aply to infection and any other gametype.