A quantitative evaluation method for the CIE color-planning activity within the product design cycle is proposed in this article. The questionnaire-based process that is traditionally employed to obtain objective color psychology tends to be time-consuming. Accordingly, this study proposes the use of gray system theory to overcome this problem. In the CIE color system, colors are defined by three primary colors, R (red), G (green), and B (blue). Using these three principal hues with fixed equigap sequences to simulate specific basic color samples is an efficient means of investigating unicolor images on a personal computer. However, a gray relational generating operation can be used to simulate colors beyond these basic samples and to predict the corresponding membership values for semantic words. In addition, the gray clustering operation is introduced to predict the overall color image evaluation of multicolored products. The predicted evaluation results of the gray system theory and a back-propagation neural network are both compared with experimentally verified results. The results indicate that the gray forecasting model is the more effective means of predicting the image evaluation, and therefore, the method is adopted within the color-planning activity. Although this study takes the example of the Internet-aided color planning of a baby walker as a case study, the proposed method can also be used on other products. (C) 2004 Wiley Periodicals, Inc.