The walls of Oplontis, when not covered in murals, are covered in the remains of murals. There are a lot of scratch marks that are the remains of the sketches for murals.
Oplantis is a Roman villa not far from Pompeii. It was covered in the same volcanic eruption, but wasn't rediscovered until about 15 years ago. The villa belonged to the aunt of Caligula, and the frescos are relatively intact, as is the rest of the villa. All this is from one room.