I am using the alpha over node to combine 3 render layers, one with the background and some foreground elements, one with volumetrics, and one with foilage. This is my first time using render layers so this may be a common mistake but I couldn’t find anything about it. There are grey outlines around each layer and I can’t figure out why. Sorry for the bad picture.
You need to select convert premultiplied in the alpha over node in order to avoid that problem.