Mix refried beans, taco sauce, salt, and pepper together in a bowl; spread onto a large platter.
Stir mashed avocado and lemon juice together in a bowl; spread over refried beans layer.
Mix sour cream, mayonnaise, and taco seasoning together in a bowl; spread over avocado layer.
Sprinkle green onions, tomatoes, and Colby cheese, respectively, over sour cream mixture layer. Cover platter with plastic wrap and refrigerate, 8 hours to overnight.