Solid color nail art refers to the design of nails with a single, uniform color, often chosen for its simplicity and elegance. In 2021, this trend was popular, with many people opting for bold or subtle solid colors. 'High-cold' in this context likely describes a stylish, sophisticated look often associated with minimalist aesthetics. For more information, you can search for '2021 solid color nail art trends' and 'high-cold nail art styles'.