Okay, I think I might know what’s going on here… and it’s something we forgot to put in the release notes 
That’s what happens when you move so fast, heh!
If you’ve updated your site template, you’ll need to add a new elements tag to the body to ensure the colour is getting applied when it’s exported.
Your body tag in the templates might look like this…
<body {{page.bodyAttributes}}>
But it needs to include class="{{page.bodyClasses}}" so it should like like the following in your template:
<body class="{{page.bodyClasses}}" {{page.bodyAttributes}}>
Hope that makes sense, and that should fix the issue for you.