🟨 · Symbols › Shapes · Emoji 12.0 (2019)
🟨 is a plain yellow square, added in 2019 with the other colored squares.
Wordle made it famous: in shared results, 🟨 is a letter that's in the word but in the wrong place. In emoji art it's the yellow pixel for suns, stars and smileys, and on its own it reads as caution.
Paint with 🟨 in the emoji art editor, or turn any photo into emojis with the image to emoji converter.
U+1F7E8🟨\1F7E8\u{1F7E8}\U0001F7E8%F0%9F%9F%A8