Gradient colors refer to a gradual transition between two or more colors. There are various types of gradients, such as linear gradients, radial gradients, and conical gradients. Each type offers unique visual effects and is used in different design applications. Six common types of gradient colors include: 1) Linear Gradient: A smooth transition between two or more colors in a straight line. 2) Radial Gradient: Colors transition from the center to the edges of a shape. 3) Conical Gradient: Colors transition from the center of a shape to its edges, resembling a cone. 4) Angular Gradient: Colors transition based on an angle. 5) Diamond Gradient: Similar to linear gradient, but with a diamond shape. 6) Elliptical Gradient: A gradient within an ellipse shape. These gradients are widely used in web design, digital art, and graphic design.