On the wikipedia page titled Green in Islam, it is stated that:
In the Ottoman Empire, the wearing of a green turban was a privilege afforded to the descendants of Muhammad
Also, in the book Conversion and Apostasy in the Late Ottoman Empire , it states that:
Green was for muslims only
Yet at the same time, traditional clothing of various Christian communities like the Greeks and Bulgarians in Thrace, Sarakatsani and Vlachs often used green fabric to make whole garments or to use in embroidery.
Was it a law that green was to be permitted to Muslims only? Or was it just a cultural attitude held in the society at the time that was rarely policed?