This study was conducted to evaluate the effect of relative thickness of different resin composite systems using enamel and dentin shades following the natural layering concept on the final color outcome. Ninety resin composite discs were assigned according to resin composite system into three groups of 30 discs each: Ceram X Duo (S1), Filtek™ Z350 XT (S2) and Amaris® (S3). Each group was divided in to 3 subgroups (n=10) according to the relative Enamel (E) : Dentin (D) thickness in to 0.5mm E: 1.5mm D (T1), 1 E: 1 D (T2), 1.5 E:0.5 D (T3) on top of 0.5mm thick basic enamel background as a standardized layer simulating the clinical condition. A Vitapan A2 classical shade tab was used as a reference shade to which the different specimens of the three tested systems were compared. Color difference (ΔE) was measured and calculated using an electronic shade detection device which is VITA Easyshade® Advance 4.0 over a black background. UV-Shimadzu 3101 pc-spectrophotometer was also used in this study to confirm the results obtained by Easyshade Advance 4.0. The results were analyzed by analysis of variance (ANOVA)/Tukey's post hoc test (p < 0.05) ΔE. All tested composite systems at all thickness showed significant color difference (ΔE) when compared to each other with the increase of the enamel shade thickness. Although the ΔE between S2T1 and A2 shade tab was statistically significant, but clinically not perceptible (ΔE=1.780 ± 0.1814).