Combine chicken, cream cheese, mozzarella, colby Jack, sour cream, hot sauce, blue cheese, pepper, garlic powder, and onion powder in a 4-quart slow cooker.
Cover and cook on LOW until cheeses melt, 1 ½ to 2 hours, stirring after 1 hour. Stir in scallions.
Serve warm with celery sticks, carrot sticks, and tortilla chips.
