We reared hatchling Midland Painted Turtles (Chrysemys picta marginata) and Red-Eared Slider Turtles (Trachemys scripta elegans) on either black or white substrates for 120 days. Spectral reflectance of the third vertebral scute, dorsal skin of the head, and lateral margin of the abdominal scute was measured at 30-day intervals between days 0 and 120. Mean carapace intensity significantly decreased over time (turtle shells darkened) in T. scripta but did not change in C. picta in individuals reared on a black substrate. Mean carapace intensity increased significantly (turtle shells lightened) through time in C. picta reared on white substrates. Mean carapace intensity of T. scripta reared on a white substrate did not change through time. Mean intensity of dorsal head skin decreased significantly through time in T. scripta reared on black substrates. In C. picta and T. scripta reared on white substrates, mean intensity of dorsal head region skin increased significantly between days 0 and 120. Regardless of substrate color, the lateral margin of the plastron significantly darkened through time in C. picta and T. scripta. In C. picta and T. scripta reared on white substrates, reflectance spectra lines of the carapace and dorsal head skin tended to have high elevations (peaks in the 520–640 nm region). The high reflectance was indicative of a lighter green coloration relative to turtles reared on black substrates.