Hi again Wayne. I actually know someone with a solid gray/blue MC named Smokey.
From what I have read, MC's can come in any color/colors, markings, etc. EXCEPT for points (like Siamese, etc.)
The reason for this is they are what is considered a 'natural' purebred, in that they are bred for their size and personality only, and not to specific colors & markings. Anything that can occur in nature color-wise, is normal on a MC.
Solid colors are still more unusual though, so solid gray or blue won't be seen as often.
My MC Wylie, is white and orange (no tabby stripes). He has a solid white brother who has blue eyes. The guy I know with the solid blue MC, also has a sloid black MC.