Abstract: Color is one of the most important attributes in visualization design. Appropriate use of colors would enhance the effectiveness of visualization, and thus convey the intended information quickly and accurately. The perceived colors are determined by both visual stimuli and human's ability of visual perception. This paper discusses the importance of aesthetics in the visualization design and its relation to the choice of colors, and the properties of saliency, distinction, and visibility. It also relates the number of distinct colors to human's short-term memory, considers color blindness in visualization design, and finally, offers the basic design principles when using color.