A color chart for a color adjustment of a color printer and a color monitor attached to an endoscope, has a predetermined number of color cells. The color cells have the same form, and are arranged in one of a grid state and a linear state. Each of the color cells is formed by blending two colors from a group of three colors comprising red, green, and blue, according to a predetermined ratio, in an additive color process. The color cells show a gradation of color such that a color tone of each of the color cells changes continuously in one direction.