Flat Design Color Combination Taboos: Red and Blue

Quick answer：

In flat design, color combination plays a crucial role. Red and blue, while powerful, can be problematic if not balanced. Red is a strong, emotional color often associated with danger and passion. Blue is calming and often used to convey trust and stability. Combining these can be jarring and might not convey the intended message. It's recommended to use one as the dominant color and the other as an accent to maintain harmony.