What is the true color on a Pontiac 400 engine?

There's no single "true" color for a Pontiac 400 engine. The color varied depending on the year of manufacture and even the specific application (e.g., passenger car, truck). Pontiac used different shades of blue, various grays, and even some black throughout the years the 400 was produced. A restoration to factory original accuracy would require researching the specific year and model of the vehicle the engine came from.