"Quais são as cores da bandeira nacional?"

Translation: What are the colors of the national flag?

[Johnni0]

why not "Which are the colors"?

[Paulenrique]

that should also be accepted!

[neilpaul80]

Is there a rule where 'Quais' and 'Qual' used in different situations or are they always interchangable?

[Paulenrique]

Qual is singular: qual é o seu nome?

Quais is plural: quais são os seus planos para o futuro?

[ChicagoAmal]

I wrote "What are the flag's national colors"? It was marked wrong.

[morvan82]

As it should be. "What are the national flag's colors?" would be correct.

[AndersBjor8]

I wrote "What are the colours of the nations flag".
I was not accepted.
I think it should be.

[Ivitcyex]

Nation's flag is bandeira da nação.

[JuergBa]

"Banner" is also given as translation of bandeira. But it is not accepted.