"rød" is used with common nouns (feminine or masculine in Norwegian), "rødt" is used with words that are neuter in Norwegian and "røde" is used with all plural nouns. Check the tips and notes for this lesson on the web version of Duolingo.
Someday I hope they bring the Tips section to the app, because the web page hates my phone.
Does Norwegian have a similar rhyme to 'Roses are red, violets are blue' as in English?
Roser er røde,
Fioler er blå,
Druer er søte,
Og du er likeså.
Alter as needed.
The ‘d’ can also be silent. Actually I believe that the pronunciation with a silent ‘d’ is more common in eastern dialects (which is more or less the dialect of the audio). Even if the ‘d’ is silent the word is pronounced with two syllables, as ‘ø’ and ‘e’ are distinctly pronounced.