Change colour outside of GEOMETRY parameter

Is it possible to change the colour of the JPEG received in WMS when it falls outside of the GEOMETRY polygon? Currently it is white - I’d like a light greyish. I know I could change to PNG and set to TRANSPARENT but don’t want the PNG overhead. Cheers.

Actually it’s not a big issue - a transparent 512x512 PNG is only 1kb so if the the AOI is only small then its not big deal to use PNG to solve this problem.

I think BGCOLOR does what you are asking for, not?

Yeah you’re right. I missed it. Thanks!