Depends on your personal tastes. For a sleek, modern, masculine, minimalist look, you can go ahead and get them both in the same colour. Or if these are very close to one another in the home it would help to keep a theme going. Or if you are someone who really needs things to be a very close match.

Chances are the gray will be different no matter what you do. But it will be the same family of colours which is all that really matters. I wish you luck with your concrete counter tops. They are pretty cool things, but they take a certain amount of up keep that can put them in the same category as "marble" for etching and staining.

Concrete comes in all colors and particulates.

we need pictures