Saponaria officinalis is a protandrous common weed that is pollinated primarily by moths. In the male stage, the flower will be white, while in the female stage the flower will be pink. This color change is due to the accumulation of anthocyanins, a common flavonoid, in the petals. These pigments are produced via a biochemical pathway the steps of which are catalyzed by enzymes including anthocyanidin synthase (ANS). The goal of this research was to determine if the change in flower color is accompanied by an increase in expression of the ANS gene. One flower from 5 different developmental stages was collected from 10 different plants and their color quantitated by measuring light reflectance. RNA from the petals of each flower was then isolated and ANS expression was measured by using qPCR. We found that flower color did significantly increase from male to female phase flowers. Expression of the ANS gene was also significantly higher in female phase flowers. Therefore, the transition to pink in female flowers does seem to correspond to an increase in ANS expression.