Often a customer will choose the color based on where it's going to be placed.

A lightly color exterior wall or area may want the tan Sandstone Smoke Butler.
Going next to a white or lighter colored building or object the grey granite would be a likely choice.
The Millstone is charcoal in color and best matchest medium to heavy color backgrounds.

The Darker Millstone Advantage
The Millstone color is easiest to keep cleanest with it's darker charcoal granite look.