I see so much of this combination lately, and I love it.
Check out this website about color: http://www.empower-yourself-with-color-psychology.comTurquoise is a combination of blue and a small amount of yellow, turquoise fits in on the color scale between green and blue. This color radiates the peace, calm and tranquility of blue and the balance and growth of green with the uplifting energy of yellow.
On the other hand, gray is a detached, neutral color, neither white nor black or a "fence-sitter." Gray has a steadying effect on other colors. What a perfect complement for turqoise!