I had the 40" B7500 model and it exhibited the same lighter edges. I think it's due to the direct backlight leds reflecting off the sides of the frame at the edges making it slightly brighter. Although they will go through a filter to diffuse the light this model did seem to have quite a lot of unevenness from the backlight, including some Dirty Screen Effect on panning shots.
Thanks for the reply and sorry for the delay in responding.
Presumably, it's just an issue with the model and not something worth following up with Hisense.
The dirty screen effect explains my previous LG.