schwarz
black
The darkest color, the color of coal or the night. The opposite of white.
Zum Interview trug er einen schwarzen Anzug.
He wore a black suit to the interview.

black
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black
The darkest color, the color of coal or the night. The opposite of white.
Zum Interview trug er einen schwarzen Anzug.
He wore a black suit to the interview.

In colloquial language, 'schwarz' (black/illegal) often means 'illegal' or 'without official registration'. It is often combined with verbs such as 'arbeiten' (to work), 'fahren' (to ride/drive), or 'sehen' (to watch).
Er hat seine Wohnung schwarz untervermietet.
He illegally sublet his apartment.
Figuratively, 'schwarz' (black/dark) can stand for something negative, pessimistic, or ominous. This meaning appears in many fixed expressions.
Das war ein schwarzer Tag für den Verein.
That was a dark day for the club.
The idiom 'etwas schwarz auf weiß haben' (to have something in black and white) means that you have written, official proof of something. The form is always the same.
Ich möchte den Vertrag schwarz auf weiß sehen, bevor ich unterschreibe.
I want to see the contract in black and white before I sign.
The adjective 'schwarz' (black) can be used as a noun to refer to a person ('der/die Schwarze' — the Black man/woman). It is then declined like a noun and capitalized.
Die Ausstellung zeigt Werke von Schwarzen Künstlerinnen und Künstlern.
The exhibition shows works by Black artists.
In German and Austrian politics, the color 'schwarz' (black) traditionally stands for the conservative, Christian democratic parties (CDU/CSU and ÖVP).
Bei der Wahl hat die schwarze Partei die meisten Stimmen bekommen.
In the election, the conservative party received the most votes.
The verb 'schwärzen' is derived from 'schwarz' (black). It literally means 'to make something black' or, figuratively, 'to damage someone's reputation'.
Der Rauch des Feuers schwärzte die Hauswand.
The smoke from the fire blackened the wall of the house.
red
'schwarz' and 'rot' are both color words and can therefore easily appear in the same contexts, for example with clothing, objects, or signs. As colors, they are clearly different: 'schwarz' is very dark, while 'rot' is the color of blood or fire. In political contexts, both can also stand for different political directions: in Germany and Austria, 'schwarz' often stands for conservative parties, while 'rot' stands for left-wing parties. They can be confused mainly because both can have not only color meanings, but also political meanings. So pay attention to the context: is it about a color or about politics?

Zum Termin trägt Herr Schneider einen schwarzen Anzug.
Mr. Schneider is wearing a black suit to the appointment.
An der Ampel ist rot, deshalb bleiben die Kinder stehen.
The traffic light is red, so the children stop.