Calpurnia and Granddaddy made a bargain concerning the Thanksgiving turkeys. Calpurnia's brother, Travis, had been put in charge of tending to the 3 turkeys, but he did not realize they would have to eat them come Thanksgiving. He was incredibly upset, so Calpurnia decided that they could trade their turkeys for someone else's turkeys. That way, Travis would not have to eat or watch everyone else eat the animals he had made friends with.
When she could not find anyone to trade the turkeys, Calpurnia went to Granddaddy. She asked him to help her and he agreed to paint the turkeys, as evidenced on page 270:
"Next morning...you could see there were three new turkeys. They were a different color from ours, and they had fewer tail feathers...they looked about the same size and weight as our old ones."
At the end of the chapter, a comment is made about the paint spots on Granddaddy, giving away his end of the bargain. When they subject comes up about who will take care of the turkeys next year, Calpurnia determinedly volunteers, saying to the reader that this was her end of the bargain. I suspect he wants her to learn the lesson that life is survival of the fittest through raising these turkeys next year.