The combination of the two results in a deep red color. Because of the pigmentation in the clearcoat, polishes and cleaners may cause the buffing rag to turn to a light shade of red. Automatic washes tend to accumulate debris in their brushes, which will scratch your car's surface. Brushless drive throughs use strong solvents in their water, in combination with very high pressure. This will damage your surface, and sandblast scratches into the clear coat.
Preparation is the key.
Remove your mud guards, nose bras, close your windows tight, and retract your antennae. Gently spray the car from top to bottom to moisten. Despite what people tell you, dishwashing liquids are too harsh for a car's finish. You WILL damage your car's paint surface. Use a quality detergent designed for washing cars.