I'm working on a presentation using the Letterpress theme. When inserting charts or shapes, these use an image fill as a default background. These images fit nicely within the theme, and there are apparently several colors available, but I can't find a way to change them. The inspector only lets me choose a file (or a different fill method like solid color, gradient etc.). I'd expect a dropdown somewhere with the pattern image in the several different colors it apparently exists in, but can't find it. Any ideas?