Cereal crops include wheat, barley (hulless barley/qingke), oat, and rye. These crops exhibit rich genetic diversity in grain color traits, presenting colors such as yellow, purple, blue, red, green, and black. The formation of distinct grain colors is determined by the composition and accumulation of pigments deposited in cellular structures of the kernel, including the pericarp, seed coat, and aleurone layer. Anthocyanins, proanthocyanidins, and other phenolic compounds constitute the important material basis influencing grain color formation. Grain color is mainly governed by genetic factors, although external environmental conditions and cultivation practices also affect its phenotypic expression. As one of the most striking visual traits of cereal grains, grain color is a key phenotypic characteristic of crop seeds. Understanding the cytological basis and genetic mechanisms underlying grain color formation in cereal crops is of great significance for the breeding of specialty functional varieties. Currently, research on grain color in cereal crops both domestically and internationally has mainly focused on the composition and metabolic pathways of pigment substances, as well as the mapping, cloning, and molecular regulatory mechanisms of related genes. This paper systematically reviews the grain color phenotypes, grading and classification criteria based on cytological foundations, and the genetic mechanisms underlying grain color formation, discusses the application of grain color traits in crop breeding as well as future research directions, aiming to provide a theoretical basis for the genetic improvement of grain color traits and the optimization of processing quality in cereal crops.
