It has become a symbol of the Barelwis, especially Barelwis associated with Dawate Islami, to wear green turbans. Whenever you visit them, they wear green turbans and even have green flags all over the place. Their founder, Ilyas Qadri, also does the same.
The fact remains that the Prophet (sallallahu alayhi wa sallam) never wore a green turban. It is not proven in a single authentic hadith that the Prophet wore one. On the contrary, we have come to know that the army of Dajjal will wear green turbans!
Now we have a Barelwi scholar from their midst, stating that wearing the green turban is an innovation, especially how Barelwis from Dawate Islami have made this colour their mark.
The book of Mufti Ghulam Sarwar Qadri can be downloaded here: http://www.4shared.com/zip/uPEo88vn/sabz_imama__-_fatwa_from_a_bar.html
The book was also linked here, on a youtube video made by a Barelwi highlighting the difference of opinion on this issue: http://www.youtube.com/watch?gl=CO&feature=related&hl=es-419&v=HFRDzPqDeiw U kunt het oorspronkelijk boek hier downloaden: