The few C series engines I have seen apart are painted dark red on cast surfaces plus the frost plugs and also the rocker cover inside and out before final paint. The timing cover, mounts, generator and starter are black under the engine green and the oil filter cannister is light brown. Pulleys were unpainted except for green. Sump and block end plates appear unpainted except for green. The engine green didn't stick all that well to the red which may have been Glyptal.
If your engine follows a similar pattern then maybe your rocker cover is original color but it does seem a bit odd as it would have been normally painted on the engine. One thing that'd give it away is if there are sanding marks in the steel under the paint and if the blue is directly onto the metal rather than being red underneath.
The timing cover behind it doesn't look like the original paint, there were black shadows under the bolt washers and also around the front where the pulley got in the way of the spray gun.
Andy.