I would LOVE to see a silver/gray and white snake ... Unfortunately, I agree with others that a mercury pied would likely be all white, or at the very least, extremely high white with only one or two small patches of color.

Most of the cinnamon pieds and combos I've seen have been solid white with only a patch of color on the head. (Though unlike some morphs, it does seem to be a bit more variable ...)

My thought was to shoot for an axanthic mojave pied. The mojave pieds seem to have a good balance of white and color, and the color is a fairly uniform tan/gold ... Strip that of yellow pigment, and I *think* you should get a nice silver/gray.

I've got all the ingredients to make that; now all I need is, what, four generations and probably 12-15 years (minimum) of breeding ...