How to change wrapper colour

Hey guys here’s my site: https://submissionradio.com/ and here’s the page I’m looking at specifically: https://submissionradio.com/news/

I’m just wondering how I would go about changing the wrapper colour for all the pages except the home page (because there are different coloured sections that I need to keep full-width)

For those who aren’t sure what I mean, I want the colours outside of the body to be a light grey, but everything in the body to remain white.

Can anybody help? I’m a big noob, so I would GREATLY appreciate if you could show me the code to use and exactly where to put it (which PHP).

fyi, I’ve already tried going into appearance and changing the background colour, but it changes the entire background colour in full-width.

cheers!