changing a background on pages from black to white and text from white to black

Be careful what you wish for. Pages does not react to the operating system appearance mode, so when you select a blank black template for a word processing mode document, the default text will be white. However, exporting that to PDF will result in a black background PDF with white text, and most recipients won't appreciate that, especially if the goal is to print it.

Exporting a black background word processing document to Word, will result in a Word document that when opened on Windows will have a medium gray background with white text. Opening this exported Word content in Word 16.74 from Office 2021 for Mac results in dark gray text on a medium gray background with white table grid.

If you choose a blank layout template, then a Pages document can set its background color to black. The text color of an inserted Text box, or table will also be black until you change the Text color on the format panel. You will need to do this for every text box, and every cell in that table that you insert, and that is simply more work than practical. With Word 16.74 in Office 2021 for Mac, the exported Word document from a black Pages layout document will appear with black text on a white background.

There is a dedicated Pages community for these related topics.

Tested: Pages v13.1 on macOS 13.4.1