HUD symbology is focused at infinity, so there's no 'background'. The symbols and the real world are at the same hyperfocal point. Fighter pilots have been usi

HUD symbology is focused at infinity, so there's no 'background'. The symbols and the real world are at the same hyperfocal point. Fighter pilots have been using HUDs for 70 years and in the past 20 years they have become common in airliners as they hugely improve safety in low-visibility operations.