Light, a crucial environmental signal, is involved in the regulation of secondary metabolites. To understand the mechanism by which light influences carotenoid metabolism, grapefruits were bagged with four types of light-transmitting bags that altered the transmission of solar light. We showed that light-transmitting bagging induced changes in carotenoid metabolism during fruit ripening. Compared with natural light, red light (RL)-transmittance treatments significantly increased the total carotenoid content by 142%. Based on weighted gene co-expression network analysis (WGCNA), ‘red’, ‘darkred’, ‘yellow’, ‘brown’ and ‘midnightblue’ modules were remarkably associated with carotenoid metabolism under different light treatment. Transcriptome analysis identified the transcription factors (TFs) bHLH74/91/122, NAC56/78/90/100, MYB/MYB308, WRKY7/55, MADS29/AGL61, ERF043/118 as being involved in the regulation of carotenoid metabolism in response to RL. Under RL treatment, these TFs regulated the accumulation of carotenoids by directly modulating the expression of carotenogenic genes, including PSY, Z-ISO2, ZDS6, LCYB, LCYE, CHYB, CCD1-1/1-3, CCD4-2 and NCED2/3. Based on these results, a network of the regulation of carotenoid metabolism by light in citrus fruits was preliminarily proposed. These results showed that RL treatments have great potential to improve coloration and nutritional quality of citrus fruits.