Different yellow pigments can be responsible for the yellow colouration of flowers. This includes the wide-spread carotenoids, but also betalains, quinones, yellow flavonoids (some 3-deoxyanthocyanidins, yellow flavonols and yellow flavones) and anthochlore pigments (chalcones and aurones). Many popular ornamental plants, such as cyclamen, poinsettia, African violet, fuchsia, geranium, petunia, azalea and Easter lily, do not produce yellow varieties or only ivory and pale yellow varieties despite of intensive conventional breeding efforts. World-wide, there are many attempts to use molecular breeding approaches for the creation of yellow varieties of such ornamental plants. Currently, two approaches are performed; one using aureusidine synthase (AUS) from snapdragon, the others chalcone reductase (CHR) present e.g. in soybean for the accumulation of stable 6’-deoxychalcones. However, there are no reports available on the creation of prototypes showing a satisfying yellow flower colour. One of the reasons could be an unfavourable hydroxylation pattern of chalcones as the immediate intermediates for the yellow pigment formation. Previous attempts generally assumed that the present enzymes in the target plants have the ability to hydroxylate chalcones. However, recently it was shown that only specific enzymes which are not present in all plants are able to hydroxylate chalcones.