Something's going in the joint between the deck and splash. Caulk or crud. Your call.

I'd suggest Translucent Gray Axiom from www.daniclamp.com. Maybe Translucent White depending on the marble color.

Thanks Joseph- the joint is pretty tight,but you have a good point about the crud eventually building up under there! My marble has a very white background- it is not Carrara, which is more common and I know has a grayish background. Mine is "arabescato venato", ( from Home Depot) . White caulk would probably match well.

Oops - I just realized that my post above might seem like I was "dissing" Carrara when I said it was "common" , lol! I just meant that when you recommended the gray caulk, you were probably assuming that I had Carrara, since it is so popular and typically used these days! I love Carrara, but my existing bathroom wall tiles, which we couldn't afford to change, were a 1980's " bone" color , with a bone and white mosaic tile on the floor, so Carrara just wouldn't have coordinated well. The arabescato venato has light caramel colored veins as well as some light gray on a very white background, so it worked much bettter for me. It also helped that the price of was so reasonable , but I had to drive to many, many Home Depot's, and open lots of boxes, to find ones (I needed two!) with just the right colors ( some were almost all white, some only gray and white, etc) and a pleasing, uniform appearance, with no cracks or ugly black specks or other defects! That is the difference between buying mass produced vs custom when you are dealing with something with lots of natural variations like marble!