Changing page background colour of a Pages document I am creating a simple document in Pages.app consisting mostly of text. I wish to visualize it with different colour for text and page background.

While I am easily able to change the colour of the text, I am unable to do so for the page itself. Searching the Web lead me to the Apple Support document, Pages for Mac: Change the page background in Pages which wasn't useful, as I was not able to find the relevant option in Pages.app.

I am using the current latest Pages version 7.3 (5989) running on macOS Mojave 10.14.3.
Per that support document, you can only change the background colour of a Page Layout document, or one of its master pages. By default, Pages creates new documents as Word Processing documents (which don't have master pages), so you will need to select File > Convert to Page Layout before the background fill option appears.

Note that this will remove any body text that you'd previously entered, so you might need to start with a new document, convert that to Page Layout, and copy your content over.