The company flag is a symbol for the relation of the family with the home-country and north-german tradition.
The colours yellow / white represent the local department of Hannover. These are the colours of the "Welfen" the kings of Hannover.
The colour black / white / red represent the national colours. These date back to 1867 as colours of the "North German Alliance" and the first flag of the merchant navy.
The colour blue together with the colour white represents the city of Stade.