Mediates O-methylation of anthocyanins. Anthocyanins are major pigments in grapes: at ripening initiation in red grapevine berries, the exocarp turns color from green to red and then to purple due to the accumulation and extent of methylation of anthocyanins. Catalyzes both 3' and 5' O-methylation of anthocyanins, with a preference for glycosylated substrates. Active on both anthocyanins and flavonols in vitro. Most active with delphinidin 3-glucoside but also acts on cyanidin 3-glucoside, cyanidin, myricetin, quercetin and quercetin 3-glucoside. Not able to methylate flavan type skeletons with chiral centers, such as catechins or dihydroquercetin. S-adenosyl-L-methionine + a 3'-hydroxyflavonoid = S-adenosyl-L-homocysteine + a 3'-methoxyflavonoid. S-adenosyl-L-methionine + a 5'-hydroxy-3'-methoxyflavonoid = S-adenosyl-L-homocysteine + a 3',5'-dimethoxyflavonoid. kcat is 0.090 sec(-1) with cyanidin 3-glucoside (PubMed:19525322). kcat is 2.3825 sec(-1) with cyanidin 3-glucoside (PubMed:20580386). kcat is 0.118 sec(-1) with delphinidin 3-glucoside (PubMed:19525322). kcat is 0.1 sec(-1) with quercetin 3-glucoside (PubMed:19525322). kcat is 0.8976 sec(-1) with quercetin 3-glucoside (PubMed:20580386). kcat is 0.084 sec(-1) with cyanidin (PubMed:19525322). kcat is 0.112 sec(-1) with quercetin (PubMed:19525322). kcat is 0.128sec(-1) with myricetin (PubMed:19525322). Optimum pH is 8.0-8.8. Optimum temperature is 49 degrees Celsius. Pigment biosynthesis; anthocyanin biosynthesis. Expressed in berries at start ripening (veraison), when the concentrations of methylated anthocyanins begin to increase. Belongs to the class I-like SAM-binding methyltransferase superfamily. Cation-dependent O-methyltransferase family. CCoAMT subfamily.