Paintbucket on graphs is PSPACE-complete

The game of Paintbucket was recently introduced by Amundsen and Erickson. It is played on a rectangular grid of black and white pixels. The players alternately fill in one of their opponent's connected components with their own color, until the entire board is just a single color. The player who makes the last move wins. It is not currently known whether there is a simple winning strategy for Paintbucket. In this paper, we consider a natural generalization of Paintbucket that is played on an arbitrary simple graph, and we show that the problem of determining the winner in a given position of this generalized game is PSPACE-complete.