Yes. I have had the opportunity to handle a large number of OHC engines. Some were very low mileage engines in continual light use, some that were pulled and stored when relatively new (to be replaced with V8), and some that are still in use with many, many miles. The paint color does change under the influence of heat, fuel, oil, coolant and other chemical reactions.

Many of the early engines show a color change to a more green shade over time. However, metallic paint does NOT lose its metallic properties.

Oh...and at least three different factory paint colors were exhibited. A very pale blue metallic, a turquoise-blue metallic, and a turquoise blue non-metallic. Along with some having black ribs from the factory, others not...