The reds, the purples, and their blended combinations that decorate autumn foliage come from another group of pigments in the cells called anthocyanins. Unlike the carotenoids, these pigments are not present in the leaf throughout the growing season, but are actively produced towards the end of summer.[1] They develop in late summer in the sap of the cells of the leaf, and this development is the result of complex interactions of many influences – both inside and outside the plant.