One day I was in Düsseldorf airport to take a flight. I had already checked-in online and only had the barcode on my phone.
When I arrived at the security checkpoint to scan my barcode, it didn’t work. I was already late. I tried every zoom, rotation… nothing. The security guy told me I needed to go back to the check-in gate and hope they were still there to print a paper boarding pass.
But then I realized: my phone was in dark mode, and the barcode was shown with dark as foreground color. So I just switched to light mode… and it saved me time, my flight, and a lot of stress.
A reader that assumes dark-on-light is a reader that works everywhere except on a phone at night, which is where boarding passes actually live. Foreground colour is a setting in every serious imaging library — including the Aurora Imaging Library I work on — and it costs nothing to set it correctly.
I still switch to light mode before every gate.