<font face="Verdana, Arial, Helvetica, sans-serif" size="2">Originally posted by speedbird2018:
boarding passes issued by a kiosk, are printed in red. This is to alert the gate staff to the fact it was a remote check in.</font>
Initially that was the case... but now every other machine uses black ink and generally the boarding passes have an 'e-service' watermark. I suspect this is used to alert staff now.