The colors of those flags represent the symbols and ideas.
If I am right, black stands for their Pan Arabism, Red stands for the Baath party, Green stands for Islamic heritage and so on.
something like that -- plus the Egyptian flag features the eagle of the Caliph Saladin, the Syrian flag is a remnant of the Arab Republic which was a union of Egypt and Syria while the IRaqi flag is similar to the Syrian only with Allahu Akbar written between the stars and 3 stars to represent the 3 provinces