Rationale: A lot of use cases for the barcodes/QR codes are for things that will inevitably be displayed on a screen to be scanned. Currently the background is transparent, which works well for some cases, but in a lot of cases they get displayed against a browser/app's default background colour, which can include dark colours.
Here's an example... depending on screen brightness and such you might not even be able to see that it has a QR code in there somewhere.
It would be good if there was a tick box for a "white background" with transparent being left as the default for existing use cases.