Halsey Custom Sidebar Background Colors

Good Morning
One of my clients needs me to change the background color on one of the sidebars in the Halsey theme. I’ve been told that ‘due to some peculiarities of the page structure, you cannot set a custom background color for the right/left sidebar.’

Surely there is a way around this. It may not be easy but there must be a way I can do this. Has anyone any ideas?