I am not a contractor m, but this was easy to figure out. If you’re hanging dark wallpaper, color match the darkest background color and paint a strip on the wall where your seams will be. When this stuff dries, you can catch the tiniest glimpse of the edge of the paper or wall behind in some small spots. I touched up with a paint wash to “dye” the slight white seams. I’m a little obsessive about the details. Turned out nice but the room isn’t finished. Here’s a peek at the progress.