Purpose: In addition to the CIE Lab color-difference formula (∆E*_ab), advanced formulas that include weighting functions have been introduced. The objectives of this study were to determine the correlations in color differences between different shade pairs of resin composites by different color formulas, and to determine whether the weighting functions included in the advanced formulas influenced the color-difference values. Materials and Methods: Color was measured after polymerization of two resin composites in 26 shades, and color differences between shades were calculated by ∆E*_ab, CIEDE 2000 (∆E₀₀), and DIN 99 (∆E₉₉) formulas. Regression analyses were performed between the color differences calculated by three formulas in each group divided by the differences in color parametric factors between the pairs compared. Results: There were significant correlations between ∆E*_ab and ∆E₀₀, ∆E*ab and ∆E₉₉, and ∆E₉₉ and ∆E₀₀ (r² = .99, .89, and .90, respectively). The weighting functions in the CIEDE 2000 formula had influence on ∆E₀₀ values when differences in chroma and hue between compared pairs were great. Conclusion: Differences in parametric factors between the pairs compared influenced the correlation between ∆E*_ab and ∆E₉₉values (r² = .25 to .97). As the CIEDE 2000 formula has been proven to be better matched to observer responses and showed significant involvement of weighting functions compared to CIE Lab color difference, this formula should be considered for evaluation of the color of resin composites. Int J Prosthodont 2005;18:150–155.