On my laptop and phone I can tell the two apart both together and with some distance between them when in relatively isolated blocks with similar surroundings. I might struggle if one were surrounded by brighter colours than the other, though human visual perception had trouble with that anyway (hence the "those two colours are actually the same" optical illusions).

The screen I code/write/read on mainly is setup differently to be easier on the eye for long periods but is not as true in colour output, I think (I'm away from it right now so can't check) they may look nearer identical on there.

I suspect people reporting difficulty seeing the difference will be a mix of differences in their eyes and differences in they screen configuration (or screen quality: some things can't be configured around).