Exposing broiler chicken eggs to light during incubation can influence hatchability, stress levels, and overall chick welfare after hatching. Therefore, this study aimed to determine the effect of different-colored lights applied during incubation on serotonin and corticosterone hormone concentrations related to post-hatch chicken welfare. Gerze Turkish Indigenous chicken eggs were incubated under no light (dark; n: 108), green light (n: 114), red light (n: 114), and white (n: 114) light for 18 days. All chicks from each treatment group were fed for 120 days. Plasma corticosterone levels were evaluated using a commercially available ELISA kit (detection range 0.1-40 ng/mL, Chicken Corticosterone ELISA ^{BT LAB}). Plasma 5-HT levels were also measured using a commercially available ELISA kit (analytic range 0.5-150ng/mL, 5-HT BT LAB Chicken Serotonin ELISA Kit), following the standard procedures. Red-light-incubated chicks had the lowest (P<0.05) plasma corticosterone. Dark-incubated chicks had higher (P<0.05) plasma serotonin concentrations than green- and white-incubated chicks. However, green-incubated chicks had lower (P<0.05) plasma serotonin concentrations than red- and dark-incubated chicks. These results indicate that different-colored light applications during incubation altered post-hatch serotonin and corticosterone concentrations. This work was supported by the Ondokuz Mayis University (Project no: BAP04-A-2024-4803) Scientific Research Coordination Unit.