To sort through the chaos of modern dating, some taxonomically minded singles apply a color-coded system to potential partners. Red flags are behaviors to avoid (deceit, poor dental hygiene). Green flags are go-ahead signs (honesty, owning floss).

So what is a beige flag?

According to the TikTok users who have latched on to the term in the past month, a beige flag is an odd trait in a romantic prospect that is not quite a deal breaker, but not exactly a plus, either.

Dunking Oreos in water instead of milk is a beige flag. So is turning on caps lock to type the first letter of every sentence, or maintaining a Lego obsession into adulthood, or being afraid of astronauts.

Benign but baffling, they are the kinds of things that might come up in a gentle roast. As one user put it, a beige flag makes a potential partner or a partner pause and say “Huh?” for a few seconds before carrying on with the relationship.

“Everyone has their beige flags,” said Marisa Bertani, 29, an actor in Los Angeles. For example, her girlfriend of over a year moves her couch to a different spot in her apartment roughly every two weeks. Ms. Bertani said she did not mind the habit, but she did not understand it, either. “I’ve never met anyone in my life that can think of so many ways to rearrange a living room,” she said.

She posted a video about her partner’s quirks on TikTok, where the hashtag #beigeflag has more than half a billion views. The videos, which are often set to a schmaltzy saxophone soundtrack, function as a kind of humblebrag: They appear self-effacing while still serving as a flex of the poster’s relationship status.

Beige flags are just as subjective as the other ingredients in compatibility soup, said Kimberly Moffit, a therapist in Toronto who specializes in dating and relationships. What is adorable to one person will almost certainly be repellent to someone else, she added.

That beige flags are debatable may have helped the term take off on TikTok, a platform that prioritizes engagement. Many of the videos are accompanied by heated comment sections, some of them tens of thousands of messages long, in which viewers weigh in on just how peeved they would be by the trait in question.

Kallie Fockler, 19, a barista in eastern Ohio, watched one video in which a woman describes her boyfriend’s habit of eating live ants he finds crawling around his house as a beige flag. “To me? Total red flag,” Ms. Fockler said. (Many commenters agreed, although eating insects is common in many cultures outside the United States.)

Ms. Fockler posted a similar video about her own boyfriend, who struggles to remember plans but can retain a seemingly unlimited number of facts about sharks. Ms. Fockler is charmed by his encyclopedic knowledge of fin shapes, but some commenters on her video were not.

“I’ll take the sharks,” she said, “as long as you’re not eating ants.”

The newest shade of flag has entered a sprawling lexicon of dating terms that is expanding as more people discuss their love lives online. Definitions are in flux: In a video posted on TikTok last year, Caitlin MacPhail described beige flags as things that come across as boring on a dating app profile — like alluding in any way to “The Office.” “If you’re looking for the Pam to your Jim, I’m just going to assume you have no deeper meaning,” she said.

But the term has evolved into something weirder. “My husband’s beige flag is when he acts like he’s going to give me a kiss,” one user wrote in a video posted last month, “but he’s really hiding a whole strawberry in his mouth and then proceeds to push the strawberry into my mouth.”

Lamont White, a dating coach in Atlanta, said it was good for partners to discover each other’s beige flags. In the long term, we need to know if we can stomach a person’s oddities — and vice versa. “Guess what?” he said. “You have beige flags, too.”

Ebony Jasmine Harris, 26, a content creator in Sarasota, Fla., thinks that anyone who denies having a beige flag is lying. Hers is that she refuses to save the phone number of anyone she’s dating. “It is a little confusing,” she admitted. “Sometimes I don’t know who is who until I text the conversation.”

When talk of red flags dominated TikTok, Ms. Harris said, she had started to feel discouraged about the dating scene. Beige flags have ever so slightly brightened her outlook.

“Maybe there’s a little hope,” she said, “that I’ll just end up with somebody weird.”