Cycles doesn't preview. Cycles materials show up in all white.

Cycles materials that also have a Firefly root node (e.g. a PoserSurface root) will preview using the Firefly root, not the Superfly root, even if Superfly is the selected renderer. But that's only true if "enable hardware shading" is unchecked in the preview settings. If it's checked, they preview in all white. That's with OpenGL. If you pick the Sreed preview option, it always uses the Firefly root regardless of that setting. (It's possible this has changed in newer updates? But I haven't noticed anything.)

If you are in one of the scenarios where the PoserSurface root is being used, it can give an all-black image for some invalid situations, e.g. you have a Diffuse_Value of 0. You might be thinking it has something to do with your Cycles shader nodes, but it doesn't.