I got the black steel Elemats for my E with a grey floor. I like it MUCH better with the black, looks industrial. But, the Elemats have coordinating cup holder liners, etc, so the whole floor and dash shelves are black. Ithnk black and grey would be distracting.
I have the grey and they deffinately show more dirt and scuff marks. I have a set of black weather tec mats that i bought back in 98 and they look new compared to the mats in the E. In an older E i would go with the gret mats since they fit better in the back seat. The newer black mats dont have the piece that slides under the front seats.