The correct answer to "彩虹的微笑" in English is "smile of the rainbow".
In English, "smile of the rainbow" is a poetic way to describe a beautiful and radiant smile, just like the colors of a rainbow. It implies happiness, positivity, and joy. The use of the word "rainbow" adds a touch of enchantment and magic, evoking imagery of the vibrant and diverse colors that make up a rainbow. This phrase can be used to compliment someone's smile, particularly when it is vibrant, filled with warmth, and spreads happiness to those around. "Smile of the rainbow" is a creative way to express the beauty and impact of a genuinely happy smile.