It wasn't that the valve covers were the wrong color. As stated by others, the entire engine is the wrong color. The valve covers are the wrong style, they're from a later model engine. I'm also a bit confused by the intake manifold on your engine. I'm not sure what I'm seeing. It looks like a single plane 4 bbl intake. As far as I know, these were only used on 273's but it could have been switched onto a 318. It's also possible you could have a 2 bbl manifold with a 4 bbl adapter & carb mounted on it. I just can't be sure from the pic you posted.
