When I render with the freestyle feature in cycles, some edges are not outlined. This image was rendered with the default freestyle settings other than the line style, which was changed from stroke to color. How do I fix this?
You have to construct a Line Set by including/excluding characteristics of the object in the view.. the default is not serving your purpose, here. If necessary, you can explicitly select edges to be stroked by CtrlE : Edge Menu > Edge Data > Mark Freestyle Edge.
Here, I've just increased the Crease Angle ( a threshold value ) in the Freestyle settings....
but there are no end of options. I'd recommend playing with them using the Blender Internal renderer, so you get immediate feedback in the viewport. The settings will still be available when you switch back to Cycles.