MidgePhoto on Nostr: Laser printers put a pattern of charge onto a roller, which then collects toner, or ...

Laser printers put a pattern of charge onto a roller, which then collects toner, or transfers the charge to a film which collects toner.
So if the roller were not holding a charge, or had a pattern of charge other than that intended by the attacker, the yellow dot message would be harder to read.

I once saw a Brother where two of the toner cartridges had been swapped. The transposition of colours was amusing.

I suppose yellow paper is available, but the toner would show.