The functional aspects of many of the consumptive products used in our daily lives are now fully matured. Consequently, enterprises seeking to develop new products are now obliged to place an ever-increasing emphasis on a product's apparent style, i.e. its color and form. However, conventional numerical approaches are limited in their ability to ascertain an individual's psychological reaction to a particular product style. A mutual dependency exists between a product's form and its color when considering the overall image sensation of the product. Accordingly, a quantitative evaluation method using gray theory for the CIE color planning stage of product design is proposed in this paper. Subsequently, this paper further develops an approach to evaluate the integrated image of a multi-colored product form based on the theorems of fuzzy neural networks and gray theory. Two case studies are taken to demonstrate the effectiveness of the image evaluation approaches for the product color design and the multi-colored form design.