First of all, one of these two concepts is a team game with red and blue teams. For team games, we have two options, really: Make team skins for ships (a lot of work), or make the red team use red thruster effects and the blue team use blue thruster effects (not a lot of work, but not so easy to distinguish teammates from enemies).
Spaceball: Similar to UT2004's Bombing Run mode. A ball is placed in the center of the field. You pick up the ball by flying into it. Once you have the ball, firing secondary weapons will shoot the ball. Running into or being hit by a shot ball will give you the ball. Thus if you're in trouble, you can pass the ball to a teammate. The ball carrier would be distinguished by a colored aura or some similar effect. There is a goal on each end of the playing field. By shooting the ball into the enemy goal, you score a field goal, worth 3 points. By physically flying into the goal, you score a touchdown, worth 7 points.
Turkey Shoot: Players cannot hurt each other in this mode. In Turkey Shoot, the game spawns wave after wave of AI enemies for the players to destroy. There is a time limit to this game. When you die, you're out for the remainder of the round. When time runs out, the person with the most kills wins. If all players but one die, the last player still alive wins.