The Flag for Islamabad - National Capital of Pakistan - is primarily based on the National flag of Pakistan. The diagonal design is to differentiate it from the National flag. The square shape is to make the triangles symmetric. The star and crescent are 'regular' as in the national flag. The black colour is added to give it a distinct look. Black was the colour used for the flag at the time of the conquest of Makkah by the prophet of Islam, Muhammad.