Naturally brown-colored upland cotton is used in specific textile industries. The color results from condensed tannin formed by proanthocyanidin (PA) oxidation. However, the roles of PA biosynthesis and glucose metabolism in brown pigmentation are unclear. Here, we integrated proteomes and metabolomes of fibers collected at 0, 10, 20 and 30 days post-anthesis (DPA) from a brown-colored cotton line (Z161) and its near-isogenic white-colored cotton line (RT). Compared with in RT, all the proteins in the flavonoid biosynthetic pathway in Z161 were highly accumulated. The metabolome data showed that the epi-flavan-3-ols in most of the brown fibers. Significantly lower levels of catalytic enzymes of the starch and sucrose metabolic pathway, which affects cellulose biosynthesis, were found in Z161 compared with in RT, except endoglucanase and uridine-5'-diphosphate (UDP)-D-glucose pyrophosphorylase