One of the five colours the emoji keyboard started with

On Snapchat, the yellow heart means something exact: it's the badge the app shows when you and another person are each other's number-one best friend, the top of a small hierarchy of friendship emoji the platform assigns automatically. A generation of users learned the colour's meaning from that system before they ever thought about it consciously, which is why yellow reads, more than any other heart, as friendship rather than romance.

Off Snapchat the association loosens but doesn't vanish. Yellow is the colour of sunshine and easy warmth, so the heart tends to accompany cheerful, uncomplicated affection — a birthday note, a thank-you, a message to someone you're fond of but not dating. It's the heart you can send a coworker without raising eyebrows.

The thing to watch is that its meaning is genuinely regional and generational. Where a heavy Snapchat user sees "best friends," someone else may see nothing more specific than a happy heart. That gap is small, but it's real, and it's a good reminder that coloured hearts carry dialects — the same glyph can say slightly different things depending on who's reading and where they learned it.