Grey bars instead of black

[Cinemaddict]

Up until a few months ago, whenever I played 4:3 video on my BD-player, there would be black bars on either side. For some reason, they are now gray bars. I find these rather annoying.

My player: Panasonic BD-80

I know it's the BD player and not the TV, because I have tried it on multiple TVs.

Does anyone know how I can change it back to gray?

EDIT: I have looked through all the settings but haven't found anything.