Yup, get out your checkbook. Automotive paints contain UV absorbers and free radical quenchers. O'Donnell says even though the technology is there to make paint and colors last 100 years, it would not be a wise investment for homeowners. Most folks tire of a color in 20 years or less, and decide to repaint. If the paint is over-engineered, the consumer will no longer be getting good value for the money.
Pigment used in high concentrations is more stable.
The irony is organic pigments have a very poor hiding ability. White is added to these colors to make them more opaque. Both clear and opaque oil-based finishes tend to yellow in low light. With time, the oil in the paint yellows as it picks up trace heavy metals or forms enough double bonds, making a molecule that looks yellow. When you expose the paint to light, the UV-generated free radicals disrupt these molecules and the yellow patina subsides.