The dried bilberry powder is not a mandatory ingredient, but it helps to naturally enhance the purple colour of the panna cotta. The North American variety of blueberry has a light green flesh, as opposed to the dark purple pulp of European bilberries. Panna cotta made with blueberries may result quite pale in colour, as compared to the same recipe made with bilberries. Instead of adding artificial colouring, the powder of dried bilberries is added in this recipe.