layer not visible (small gray circle not filled in)

Hi there,

I am trying out An for the first time and having some trouble--I think this is a very basic question. Some of my layers are not visible (in the screenshot, only the bottom layer is visible). These seems to be corrolated to whether the small gray circle is filled in. I can't seem to figure out how to change that (all my google searches show results for filling in shapes). Any tips?

Thanks!