The outline is showing that there is a coordinating punch (Mitten Builder Punch #127824). The punch is on the same page. The stamps are so that you can stamp a left mitten and a right mitten,but the outline shows which way the punch is oriented. There are outlines around the other "mitten parts" images in the set, too...
I'm blogging again: random.on purpose.
Within you there is a solitude and peace to which you can retreat at any time and be yourself...