This plant flowers when the leaves are not yet fully open and the plant has not yet its full size. At that time, in mid-spring the plant has a purplish color, very dark in some cases.
According to Marie-Victorin this species present a darkening in the north of its range (in Quebec).
In fact there are probably two varieties or even two distinct species, an earlier one with darker colors when young and with flowers having a longer style and hooked (Caulophyllum giganteum), and the typical species, least raise, with lighter color when flowering, but with the same size once mature, the Caulophyllum thalictroides.
At full size, this species or these species are more discreet with their green leaves and little berries, in fact they are fleshy seeds, because the Blue cohosh does not form fruit as such.