Background color modification request left / right of featured slider

Hello, Since quite some time ago, I had observed that the background colour next to the featured slider had become black instead of the blue colour I am using for mostly the whole website. Would it be possible to help how I can modify this again please? My website is: https://www.chirosintbartel.be/ The issue here reported is directly visible on top of my main page. Thanks in advance for your help. Kind regards, Bram