What does it mean to put black couplets on the door?

The black couplets on red paper are auspicious symbols, while the black couplets on white background are sacrifices to the deceased ancestors.

Most couplets are written in black on a red background, which has been handed down from ancient times. Red represents happiness, and black is because of the writing habits of the ancients, and there are no particularly gorgeous color materials. Rural people, in particular, can only write in black ink on red paper to make the coming year auspicious. As for black couplets on white background, they are sacrifices to the deceased ancestors. When handling the funeral, it will be posted on both sides of each door.