Gradual color pencil

Quick answer：

Gradual color pencils, also known as gradient pencils, are a type of drawing tool that allows for a smooth transition between colors. They are used in art and illustration to create a gradient effect on paper. These pencils have a unique core that gradually blends the colors, resulting in a seamless gradient from light to dark or from one color to another. They are popular among artists for their ability to produce a wide range of color blends and textures.