This common bi-annual weed in North-West Europe is a childhood favorite of mine. But the Digitalis Purpurea (foxglove, indeed as perfectly identified by @maxg) is very toxic. So warn your children not to play with these flowers (tempting to put one on your fingers as a thimble - and in German it has that name "Fingerhut" - fingerhat). On the other hand it makes a powerful homeopathic medication for complaints of the heart. So a very special plant indeed! Having said all this to support everybody else's enthusiam for this photograph, it is most assuredly not indigo! (but cobalt violet).