rosa
pink
The color that is a mixture of red and white; pink.
Sie trug ein rosa Kleid zur Party.
She wore a pink dress to the party.

pink
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pink
The color that is a mixture of red and white; pink.
Sie trug ein rosa Kleid zur Party.
She wore a pink dress to the party.

'Rosa' (pink) is a special adjective: it is not declined. It always keeps the form 'rosa', no matter what gender, case, or number the noun has. This is a common source of errors.
Ich suche einen rosa Pullover.
I'm looking for a pink sweater.
The figurative meaning of 'rosa' (rosy) is used almost exclusively in the idiom 'etwas durch die rosa Brille sehen' (to see something through rose-colored glasses). This means judging a situation too optimistically and unrealistically positively.
Er ist frisch verliebt und sieht die ganze Welt nur noch durch die rosa Brille.
He's newly in love and now sees the whole world through rose-colored glasses.
As a color, 'rosa' (pink) is often associated with things that are stereotypically considered sweet, delicate, or feminine. Typical nouns are 'rosa Schwein' (pink pig), 'rosa Wolken' (pink clouds), or 'rosa Bonbon' (pink candy).
Am Abendhimmel waren wunderschöne rosa Wolken zu sehen.
Beautiful pink clouds could be seen in the evening sky.
red
'rot' and 'rosa' are both color words and are close to each other. 'rot' is the strong color you see, for example, in blood, cherries, or a red traffic light. 'rosa' is lighter and softer, like a mixture of red and white. You can confuse them when an object has a light shade of red. As a simple guide: strong and clear is 'rot'; light and delicate is 'rosa'.

Im Büro hat Max eine rosa Karte auf den Schreibtisch gelegt.
At the office, Max placed a pink card on the desk.
Für den Notausgang hängt ein rotes Schild an der Tür.
There is a red sign on the door for the emergency exit.