The middle is a gradient color

Quick answer：

Gradient colors are used in design to transition smoothly between two or more colors. They are often used to create depth, emphasis, and to blend colors seamlessly. In web design, gradient backgrounds can be used to enhance the visual appeal of a website. In art, gradients can be used to depict light and shadows, or to create a sense of movement. In photography, gradients can be applied to adjust exposure and enhance the overall look of an image.