The colors of Shia Islam are red, black and green.
The background of red, the color of Justice, is as follows. The Arabs had a tradition of placing a red flag on the grave of a murdered person who was not avenged. When relatives or friends avenged the murdered person, the red flag on his grave was changed to black, the color of mourning. Red flags are placed on the graves of the Shiite Imams (A), who all fell as martyrs at the hands of tyrants, because their blood has not yet been avenged. When the Mahdi (A) comes and takes revenge, the red flags will be replaced by black ones.
Who will the Mahdi (A) avenge? Here we come to the doctrine of raja’at – “The Return”, which is in the realm of green – the color of esoteric Islam. According to it, before the end of the world, Allah will return to earth both the most righteous and the most evil, so that retribution can be carried out. The Prophets and Imams (peace be upon them all!) will return, and their oppressors and all the tyrants of the nations will return.
Imam Sadiq (A) said:
“Have they not heard what my grandfather, the Messenger of Allah (PBUH), said and what we, Ahl al-Bayt, have repeated many times about ‘raja’? Have they not heard this verse: ‘And We will make them feel the lowest punishment and the highest punishment.’ The lowest punishment in the verse refers to the punishment that they will receive on the Day of Raja’ (return), and the highest punishment refers to the punishment of the Day of Judgment.”
“We wanted to show mercy to those who were humiliated on earth, and to make them leaders, and to make them heirs” (28:5).
Imam Sadiq (A) says:
“By Allah, the tanzil (historical reason for the revelation of this verse) is the children of Israel on the day of salvation from Pharaoh, and the ta’wil (esoteric meaning) of this verse is us, Ahl al-Bayt, on the day of raja’ah.”