Involved in anthocyanin and protoanthocyanidin biosynthesis by catalyzing the oxidation of leucoanthocyanidins into anthocyanidins. Is able to synthesize anthocyanin pigments from leucoanthocyanidins in aleurone tissue. Converts dihydroquercetin to quercetin in vitro. 2-oxoglutarate + a (2R,3S,4S)-leucoanthocyanidin + O2 = a 4-H-anthocyanidin with a 3-hydroxy group + CO2 + 2 H2O + succinate Binds 1 ascorbate molecule per subunit. Binds 1 Fe(2+) ion per subunit. Pigment biosynthesis; anthocyanin biosynthesis. Plants over-expressing ANS1 have increased accumulation of a mixture of flavonoids and anthocyanins, with a concomitant decrease in proanthocyanidins, and could represent an enhanced antioxidant potential. Belongs to the iron/ascorbate-dependent oxidoreductase family.