Story Update:

I asked the eBay seller who sold me the "black" insulator a couple of weeks ago if he had any more. Not being a very verbose person, apparently, he wrote back "i got 1". So, I asked him about it, whether it was the same type, could he tell what color it was under the soot coating, etc.. He didn't seem interested in any details or in telling me anything, so again, knowing what the color was was not going to be an option. It's just another odd item among the thousands of things he's sold on eBay. Another wordy email back from him: "same type. send me $20 i'll ship it". So I did. And he did. And here it is. The one on the right.