Using WPF, draw triangle with different colors at vertices

Question

Using WPF graphics (XAML or code), I would like to create a 2D or 3D triangle with different colors at the vertices (say red, green and blue) and interpolated colors elsewhere inside. I'm guessing DrawingBrush might be the way to go, but I don't know how. I would rather not use texture mapping which (it seems to me) would be overkill.

Thanks,

Tom