This study assessed and characterized discoloration when white MTA (wMTA) was placed in the coronal aspect of the root canal ex vivo and the influence of red blood cells on this discoloration.Canals were prepared from the apical aspect and restored with either wMTA + saline (n = 18), wMTA + blood (n = 18), or controls (n = 4 + 4) (blood or saline alone). Color was assessed according to the CIE L*a*b* color space using standardized digital photographs at 3 time points: baseline, day 1, and day 35. Statistical analysis was performed by using 1-way analysis of variance and a 2-sample t test with P < .05.All teeth discolored when restored with wMTA, which was most prominent in the cervical third of the crown. The presence of blood within the canal adjacent to the setting wMTA exacerbated the discoloration (P = .03).wMTA induces the gray discoloration of the tooth crown, and the effect is compounded in the presence of blood.