Well you are able to access any of the hundreds of color settings in the current theme. You also can access any of the brush resources that our theme defines and uses throughout the product, although we need to add a documentation topic for that yet. Maybe we can get that in for the next release as well.
If you have any other related features than those that you'd like to see, please let us know and maybe we can get them in for the next release as well.
If you describe your button animations/3D a bit more, I can reply with an implementation recommendation. But you are correct, any control can be added to the Ribbon that implements the IRibbonControl interface. If you are building one from scratch, inheriting our ControlBase is probably a good idea since it already implements much of the interface or if you are doing a button, then perhaps from Button (in the Ribbon.Controls namespace).