It depends on what type of treats. If it is watermelon, cantelope fresh veggies and such I throw it on the ground. If it is scramble eggs or any kind of oatmeal or yogurt stuff like that it goes in the white bowl. They know the white bowl.
I like to keep scraps out of the run, so if they reject anything it doesn't sit there and rot. Anything dry goes right on a big flat paver that sits between the run and one of my composters. Wet stuff goes on a paper plate, normally one I've already used in the house for something. Anything the chickens leave gets tossed right into the composter, soggy plate and all.