What logic are you using to pick up the objects? If you're using drag/drop behaviour then this shouldn't be a problem as it will pick one at a time, but maybe you're not using that. Anyway since you're having a problem with it, look into Pick top/bottom condition on the object, you can pick the top object each time so one at a time.
Edit: I just realised that your problem is you want to pick up one 'type' of object at a time. You can still pick types by giving red/blue instance variables type=red and type=blue to distinguish between them. Then you would pick up all with type=red or whatever fits the game.