This is the 540th most frequent Norwegian word.
blå
Blue.
In this context, 'blå' describes the color of the sky, used as an adjective.
Himlen er blå.
The sky is blue.
Here, 'blått' is the neuter singular form of 'blå', agreeing with the noun 'kort' (card), serving as an adjective with agreement.
Han fikk et blått kort i fotballkampen.
He received a blue card in the soccer match.
'Blåtur' is a compound noun where 'blå' figuratively implicates mystery or spontaneity.