Hi @HughN. As a suggestion you could always add a bit of code to change the browser (page) colour. I’ve just tried it and it seems to work. You won’t see the background colour in the Blocs app, but you will when you preview the page/site in a browser. Here’s what I did:
1/ In Blocs, click on the Current View Page Settings (Cmd + Alt + P)
2/ In the Page Settings dialog box click on the Add Code Button.
3/ In the Add Code dialog add this code to the Header:
4/ Click the Done button.
5/ Save your project and preview in a web browser.
Obviously change the Hex Colour to your own colour value.
I’m sure there will be smarter ways to do what you want, but at least this is a solution for the time being.