What is the symbol of Spring Festival couplets?

Door numbers, also known as hanging doors, are made of five-color paper. It is an ornament hung on the threshold during the Spring Festival. Divided into red, yellow, blue, purple and green. The order of hanging is: red, east, green, west and yellow. Blue and purple hang between the three colors respectively. Take the door of the main hall [north] as an example. The red one hangs in the east, the green one hangs in the west and the yellow one hangs in the middle.