Zu welchem Fest tragen Menschen in Deutschland bunte Kostüme und Masken?

Why this is the correct answer

Rose Monday (Rosenmontag) is the highlight of the Carnival season in Germany, celebrated on the Monday before Ash Wednesday. Participants in cities like Cologne and Mainz dress in elaborate costumes and masks and take part in large street parades, making it the festival most associated with festive disguise in Germany.