Shvegal, the calipers were usually installed onto the axles before they were painted. When painted, the insides of them were also painted. Like you, I have to assume that something was put over the outer parts of the rotors to prevent an excessive amount of overspray. What little overspray got on the inside of the rotor was negligible. Mercedes wasn't ever concerned with overspray, runs, or 100% coverage on the axle assemblies. Even the parking brake cables were painted. It was less time consuming to paint the axles with the calipers on than not, so I'm guessing that's why they did that. Take note of the pictures below. Some are swing axles, and some show a W114/W115, but these photos are out of a sales brochure for W108/W109, W113, W114, and W115 cars. They were all being made at the same time, and since the W108 and W109 received the same front and rear axles I'm certain these pictures are representative of the W113, as well.
Look closely at the calipers. You'll see that the outsides are bare, while the insides are painted. On the other picture of the caliper from the front notice the metal brake line going to the caliper is silver while the caliper it's connected to is black. Granted, the metal lines going to the front calipers on a W113 were painted black with a light green inspection paint mark on the lower part where it attaches to the spindle. The one picture showing the caliper from the front is likely a W114/W115 car. I only included it because it shows the black painted caliper on the inside. But also notice on the other pictures where the outer part of the caliper is not painted. These are what I've always based my knowledge and restorations on. I figure a picture is worth a thousand words.
And by all means.....if any of you ever have a doubt about something I say please don't be afraid to speak up. I'm not always right, and I make mistakes every day. I don't get upset when I'm wrong about something. What would make me upset is if I typed some misinformation and it was thought to be correct. I, too, rely on all you for correctness.
And in keeping with the original intent of the exhaust manifold colors, I've added some other factory pictures of manifolds. To me they look like plain bare cast iron.
