What is the significance of the color blue in the Middle East?

Today, the color blue would be more associated with the state of Israel and so has a negative connotation with most of the Middle East's Arab, anti-Israeli population (an example of this would be the new flag that was intended to replace the old Iraqi flag, only to ultimately be rejected because of the large amount of blue that was used in the flag to represent the Euphrates and the Tigris rivers).