After reading this answer about the RTGs used on the Lunar surface, I added some of the images from the Wikipdia article Apollo Lunar Surface Experiments Package into this answer, where I noted that the Lunar soil at that location was pretty dark by comparing it to the darkness of the radiator fins of the RTG.
Then I looked up and noticed that the whole side of the LEM appears to have the texture of crinkled metallized film, but it's extremely dark! Is this a result of the landing, or was it supposed to be like that? I thought the purpose of the metallization was to reflect the sunlight to avoid the more than 1 kilowatt of light per square meter from overheating the spacecraft and crew. Did this darkening cause trouble?
I don't recall seeing LEMs so dirty - assuming this is lunar soil, was this darkening site-specific?
above: Cropped and annotated details from: "Astronaut Alan L. Bean from Apollo 12, put the Plutonium 238Pu Fuel from the Lunar Module into the SNAP 27 RTG" from here. note: red rectangle highlights possible missing "black stuff", blue rectangle highlights a shadow from a sunlit part of the "black stuff." other blue arrows show shadows cast from sunlit rods. Small blue arrows show a dark surface with bright gold circular areas suggesting a pattern of screws or fasteners perhaps.
above: "Astronaut Alan L. Bean from Apollo 12, put the Plutonium 238Pu Fuel from the Lunar Module into the SNAP 27 RTG" from here
above: Apollo 11 NASA image 1969-059C appears to be the same side of the LEM, although a different mission. The "dark stuff" is there but surrounded by bright film on either side.