01 -
Combine water and blue food color in a large bowl.
02 -
Gently crack the shells of the hard boiled eggs with a spoon without removing them.
03 -
Place the cracked eggs in the blue food coloring mixture and refrigerate for at least 2 hours.
04 -
Remove eggs from the refrigerator, peel carefully, and cut each egg in half lengthwise.
05 -
Scoop out the egg yolks and transfer to a bowl. Mash the yolks with mayonnaise, green food coloring, mustard, and vinegar until smooth.
06 -
Pipe the yolk mixture into the hollow of the egg whites.
07 -
Garnish the filled eggs with black sesame seeds if desired.