For the marinade, Hard-boil the eggs (8 min). Cool completely under running cold water and peel them. Put them in a container. Mash the beets with the juice, the vinegar and sugar in the blender’s cup. Sieve the juice over the eggs until they are fully submerged. Refrigerate for 12 hours while covered.
For the filling, Halve the eggs lengthwise, take out the yolks and put them in a bowl. Mix the mayonnaise and the vadouvan in with the yolks. Add pepper and, if desired, salt to taste. Put in a piping bag. Put the egg halves on a dish and squirt the filling into the cavity. Finely chop the parsley leaves and sprinkle over the eggs.
Preservation tip: You can dye the eggs up to 3 days in advance. Take them out of the marinade after no more than 2 days and refrigerate in a closed container. Finish the eggs completely, cover and refrigerate 12-24 hours before serving.