The story
By analogy with red flag and green flag, due to the perception of beige as a boring or bland colour. Popularized on TikTok in 2022.
First known use, by meaning
- from 2022 A clue or indication (especially on an online dating profile) that a person is boring or unoriginal.
- from 2023 A mundane but mildly unusual quirk or habit of one's romantic partner.
Etymology from Wiktionary, CC BY-SA 4.0.