The words "yellow" and "mellow" do rhyme. This means they have similar ending sounds, especially in their last syllables, which is commonly the action described by the clue "What yellow and mellow do" in crosswords like the New York Times Mini Crossword.

Explanation of Yellow

Yellow is a color between green and orange on the light spectrum, often associated with brightness, warmth, happiness, and sometimes caution or cowardice depending on cultural context. The color evokes sunlight and is widely recognized in nature and art.

Explanation of Mellow

Mellow can mean softened through age or experience, or become more relaxed and genial. It is often used to describe something that is pleasantly gentle or softened in intensity.

What They Do Together

When asked what "yellow" and "mellow" do, the answer is that they "rhyme," meaning they share a similar ending sound, which is the feature highlighted in word puzzles and crosswords.