Translation:The colors of the club are blue and black.
...If you're an Inter fan I hope you realize how badly you shot yourself in the foot there. If that was intentional then that was hilarious af.
"es" is generally for words in which adding just an "s" would make for troubling pronunciation.
I read that one-syllable nouns take -es (des Mannes) while more than one syllable nouns would add just -s (Bediener des Computers - computer operator).
"Des" is the definite article for masculine and neuter nouns in the genitive case (the case we're working on this lesson!): Die Jacke des Junges - The boy's jacket; Der Titel des Buch - The book's title. For feminine as well as for plural nouns, we use "der" in genitive.
"Den" is for masculine nouns in the accusative case, as well as for the plural nouns in the dative case: Ich esse den Apfel - I eat the apple; Ich gebe den Apfel den Männer - I give the apple to the men. This was taught on previous lessons!
"Verein" means "club"; whatever kind of it. A "football club" would be a "Fußballverein".
Why do you capitalise Blau und Schwarz and also does that mean that we can replace Verein with Club?
Why does this translate to "the club" and not "my club" since it is genitive?
If you wanted to say "the colors of my club", you'd need "die Farben meines Vereins".
Genitive case doesn't automatically imply an association with me, you, or anyone else in particular.
Clearly Duo is having trouble with possessives in this section in English. “The club colors”...not “of the” which seems a bit awkward.