Interaction Designers / UX people usually start out with low fidelity wireframe mockups for preliminary UI designs, often in a tool like Powerpoint They are done in black & white so that the commenting audience can see that they are not finished, and you are more likely to get them to constructively comment. A corollary of this is that it's time to stop collecting feedback when it gets down to discussing colours.
We're working with WPF, sometimes we use the Visual Studio designer and sometimes we use Blend. So in discussion with our UX guy today, we came up with the idea of a "wireframe" theme for WPF that we can apply to get feedback on the first iterations of the XAML storyboard. We'll be trying this out.