Molecular model of anthocyanidin synthase (ANS) from thale cress (Arabidopsis thaliana) complexed with the flavonoid dihydroquercetin (yellow), which this enzyme oxidises to quercetin. ANS converts colourless leucoanthocyanidin plant compounds to anthocyanidin and anthocyanin plant pigments. At bottom left is a molecule of delphinidin, a anthocyanidin that gives flowers and fruits a blue hue.