You might use a grill cloth or mesh to cover the bottom section with the port and woofer. Or maybe just stretch acoustically transparent grill cloth or foam over the port hole. Some people paint the insulation black immediately behind the port, which is a good look too.

I'd probably be one of those that painted the inside of the cabinet near the port flat black. To me, that's a great look, and it would probably work well with your black leather finish.