Gradient color series

Quick answer：

The 'gradient color series' typically refers to a collection of colors that gradually transition from one to another, creating a smooth and continuous blend. This concept is often used in design, digital art, and photography to create aesthetically pleasing visual effects. In the context of automotive, it might refer to the color options available for the 3 series of a particular car model, which may include gradient finishes to give the car a unique appearance.