I found a workaround for this. I had the same problem. Here is what I did:
Using FileZilla, I went into my site’s FTP at the following location:
wp-content/themes/gridalicious-pro/images
There is an image in there called bg.jpg. I copied it out to my desktop, opened it in photoshop, changed it to the color I wanted, and replaced it in the ‘images’ folder. That made it the color I wanted. My website is http://www.clevermoderns.com and you can see the light green color on there that I wanted.
I’m pretty sure that when I installed a theme update I had to go back and figure it out all over again and replace the file again, which was kind of a PITA, but I did get it to work. I’m also pretty convinced this is a bug.