Heat oven to 400°F. Spray or grease 15x10-inch or larger dark or nonstick cookie sheet. Unroll dough on cookie sheet; starting at center, press dough into 15x10-inch rectangle.
Spread 1/4 cup of the Buffalo wing sauce to within 1/2 inch of edges of dough. In medium bowl, mix chicken, celery, onion and remaining Buffalo wing sauce. Spoon evenly over crust. Sprinkle with blue cheese and Colby-Monterey Jack cheese.
Bake 12 to 14 minutes or until crust is golden brown and cheese is melted. Serve with ranch dressing.