From DDraceNetwork

Catch16 (or color catch) is a Teeworlds modification normally played with Laser, but also available with Grenade. The weapons behave like Instagib.

At the beginning of the Round every tee spawn in their own Team. The team is indicated the body and feet color. Every time you hit another player, they move in your team and gets your skin and skin colors. If all tees are in the same team, the game is over.