The use of colored LED lights is a tool for controlling the development of lymphoid organs and the immune system in general. This study aims to analyze the effects of using simple and combined colored LED lights throughout a 6 week period (1–42 days of age). In this study, 336 one-day-old chicks were used, separated randomly into four groups with different sex and lighting systems, with each group being divided into four separate replicates (4 × 21 birds). The chicks in the WL-Male and WL-Female were exposed to white LED light (WL, 400–760 nm) for 6 weeks, while the chicks in the G-GxB-BL-Male and G-GxB-BL-Female were exposed to a combination of monochromatic lights as follows: green (560 nm) from 1 to 14 days of age, green and blue (480–560 nm) for 15–28 days of age, and blue lights (480 nm) for 29–42 days of age. The use of a mixture of green and blue LED lights (G-GxB-BL) resulted in a significant decrease in the average daily feed intake and feed conversion ratio compared to white light, without causing changes in the body weight of the chicks, average daily gain, mortality rate, and coefficient of variability. G-GxB-BL lights also improved the morphological development of the bursa of Fabricius (BF) compared to white light by significantly increasing the organ index and the lymphoid follicle area. At the same time, G-GxB-BL light compared to white light improved B lymphocytes proliferation in the BF by significantly increasing the lymphocyte density in lymphoid follicles, as well as the number of PCNA-positive cells. This light treatment had these results due to the activation of melatonin receptors, which led to a significant increase in Mel1a-positive cells and a significant decrease in the number of RORα-positive cells. These results demonstrate that G-GxB-BL lights improved the growth performance and immune response in the BF of broiler chickens.