Color images are treated at various scenes, such as offices, factories, etc.. The reason is that cheap equipment can be acquired easily. In treating colors, it is important that color matches between originals and reproductions. The color of reproductions, however, differs from ones of original images, because data of input equipment are unsuitable for input data of image output equipment. Therefore color adjustments are in great demand. Generally, color mismatch between the original and the reproduction is adjusted on computers. It is possible to convert linearly or non-linearly from one color to another color. A very simple method is an application of linear polynomial (3 X 3 matrix). This has an advantage of a cost performance. But it is difficult for general users to adjust colors because there is no suitable user interface and the relation between matrix elements and reproduced colors is not well known, so the color variation could not be predicted. We studied a color adjust method, by which general users can adjust color more easily. We adopted two reasons for the coordinate conversion method for this problem. First, the color is expressed with a characteristic coordinate, which depends on an input/output equipment. Secondly, the vector expresses physical value, which assists three-dimensional thought. As a result, visual color adjustments can be achieved. Then we implement a color adjust method with a graphical user interface. Images are adjusted only by dragging the pointers.