Purpose: The purposes of this study were to: (1) investigate the correlation between thecolor difference of bilayer porcelain veneers over white and black backgrounds (ΔE1) andtheir opacity (contrast ratios); (2) determine whether there is a recommendable thresholdcontrast ratio above which the color difference is clinically acceptable (when ΔE = 5); and (3) compare the ability of porcelain veneers to mask a color change from white to blackbackgrounds (ΔE1) and their ability to mask a color change from white to clinicallydiscolored teeth (ΔE2). Materials and Methods: Forty-four maxillary anterior teeth of eightpatients with severe tetracycline discoloration were prepared for bilayer porcelain veneersin shade A2 porcelain. The cores were 0.25 mm thick. The color (CIE L*a*b*) and reflectance (Y) of the midbuccal region of each veneer were measured over white and blackbackgrounds using a colorimeter under artificial daylight. The veneers were bonded todiscolored teeth, and their color was measured after 1 week. Results: The mean colordifference ΔE1 was 10.6 (SD 2.6). The mean contrast ratio was 0.75 (SD 0.1). There was a close and statistically significant correlation between ΔE1 and contrast ratio. The determined threshold contrast ratio was 0.91. The mean color difference ΔE2 was 11.6 (SD5.5). A paired ttest showed no difference between ΔE1 and ΔE2. Conclusion: There was a significant correlation between the masking ability of veneers (ΔE1) and their opacity(contrast ratio). There was no significant difference in the ability of the porcelain veneers inmasking a color change from white to black backgrounds compared to their ability to maskthe color change from white to the discolored teeth.