Feeling Blue

An expression meaning to feel sad, dispirited or melancholy.

A frequently repeated maritime story connects the phrase with blue flags or markings displayed when a ship lost its captain or an officer during a voyage. Reliable evidence for that specific origin is weak, and the association of blue with sadness appears in English sources outside that tale.

It is therefore best treated as a general idiom with a claimed, but unproven, nautical connection rather than as an established seafaring term.