Are you talking about the grey behind the navigation, which does look textured to me, too, or the grey in the main body, which is what I thought you meant? Both are done with small repeating images, anyway.
It does have a tiny texture repeating, 4px by 4px .png which you can just see here:
It's basically just a grey square with a darker grey cross in it. I'm not sure if there is a particular name for it apart from seamless repeating pixel tiles.
@bo5ton , can you re-attach the image? I think I accidentally deleted instead of approving it. My apologies.