Porcelain restorations have double-layer color effects resulting from the presence of body and opaque layers. The purpose of this study was to quantify the color differences resulting when a defined thickness of body porcelain is fired on an opaque porcelain of the same shade designation and from the same porcelain brand. A color difference coefficient was defined as the color change resulting from a 1-mm-thick layer of body porcelain on an opaque porcelain of the same shade and brand. Six shades and four porcelain brands were evaluated in this study. The range of color difference coefficients for all shades and brands was 6.76 to 14.32. There was no significant difference between shades or between brands. The use of color difference coefficients is a practical method of evaluating porcelain shades and brands and should provide guidance in the choice of porcelains and the fabrication of porcelain restorations to better achieve the desired esthetics.