With a roof like that, I would think it would have an electrochromatic tint on it. Flip a switch, it turns opaque. Flip it again, it's clear. IIRC, they're usually made by sandwiching polarized crystals between two layers of glass. Apply a current, the poles align, and presto! you have clear glass. Turn off the current, the poles revert to a random arrangement and you can no longer see through it.