The Top Panels for the 7000 series cases are 500mm x 188mm (22 7/16" x 7 7/16"). The 7000X comes with the glass panel (shown on the left) and the 7000D Airflow comes with the steel mesh (on the right). Like the front panels, the tops are fully interchangeable - you can get the Airflow panels and put them on the 7000X (or vice versa). You can get different colors - there's no reason why you couldn't put the black panels on a white case - it might actually look pretty cool. You can also switch out the panels by season - use the airflow panels for the hot season (summer here in Texas, winter in Oz) and the glass panels for the cool season (about 3 months here).
You can get the different panels on Corsair.com:
7000D Top Solid Panel - Black
7000D Top Solid Panel - White
7000D AIRFLOW Top Panel - Black
7000D AIRFLOW Top Panel - White
7000X Tempered Glass Top Panel - Black
7000X Tempered Glass Top Panel - White