XPS 15 7590 OLED - how do I know it's an OLED?

I know the topic sounds dumb but I'm getting skeptical here.

I bought the exact same laptop that some colleagues use at work (or so I thought), and it just got delivered. The blacks on those screens are amazing, but when I check mine against a black picture (or the default red flower one) I can clearly see a difference between the bezels and the screen. Even at lowest brightness.

Is this normal, have I received the wrong model, or am I missing settings somewhere?