Keep the sections grey Jon, imo the contrast will work well with the 540i's dark interior
if it was me I would dye parts of the door cards black to match the seats
Keep them as they are and fit the matching door cards.
All black interiors can look a bit dull
Only just seen this, and someone has beaten me to it. I was going to say to keep them as they are and then add some contrast to the rest of the interior by changing the strips to silver, or a colour that better matches the light part of the seats.
All black seats get a bit hot in summer