when something has a large loss, the same process as mending a tear is used. however, this leaves japanese tissue visible on the face of the object (here: posters). if the loss is in a margin or a large white space this isn't a problem, but in the case that the loss is in a colored or dark area of the poster it stands out quite a bit. to keep the mend from being a distraction, it can be filled. all this means is that the area is toned, here using colored pencils. this way it's still visible as a loss (the texture difference alone would make it obvious), but it doesn't distract the viewer from the rest of the image.