Blue-red-white first-second-third ribbon placings are the standard convention at American county and state fairs, used across livestock, produce, and home-arts judging alike. "Best in show" or "grand champion" ribbons (often purple or rosette-style) sit a tier above a simple first-place blue.
The phrase "blue-ribbon winner" has become general English for "the best of its category" well beyond fairs themselves, but the literal ribbon-color convention is where it comes from.