I happened to have this book that I bought last year when his IEP was written. It never got used...Will could have cared less. Guess what? It was perfect for ABA. It has simple pictures, like a picture of a carrot, with a white circle in the middle. The child is supposed to find the color that matches and then fill in the white circle to match the rest of the picture. I would imagine you could make these with your computer fairly easily. I plan to when these pages run out.
sample page from Kumon
At any rate, it worked beautifully. He was playing with a favorite toy at the table, so we switched out the favorite toy for the coloring. Once he finished the coloring, he got the toy back to play with. He sat today at the table almost the entire 30 minute session! He's made a lot of progress already!