Ive seen few Islamic sects, always wearing green turban and white clothes, or all green clothes, stating it as to be following Sunnah of Prophet Sallalahualayhi wassalm. What is the context behind it?.
Praise be to Allaah.
The basic principle with regard to clothing is that it is permissible and the Muslim may wear whatever colour of clothing he likes, except that which was forbidden by the Prophet (blessings and peace of Allah be upon him), which is red and yellow. The best colour that a man may wear is white, because of the hadeeth narrated by Ibn Abbaas (may Allah be pleased with him) who said: The Messenger of Allah (blessings and peace of Allah be upon him) said: Wear white garments, for they are among the best of your garments, and shroud your dead in them.
Narrated by Abu Dawood, 3380; at-Tirmidhi, 915
For more information see the answer to question no. 72878
It says in Fataawa al-Lajnah ad-Daa'imah, 24/18: It is proven that the Prophet (blessings and peace of Allah be upon him) preferred white clothing over other colours. With regard to other colours, there is no proof that any of them are preferred. What is prescribed for the Muslim is to wear that which will cover him and not to go to great expense in doing that. This is the teaching of the Prophet (blessings and peace of Allah be upon him). One should also avoid wearing clothes of fame and vanity, and anything that resembles the clothing of women or disbelievers, or anything that is contrary to Islamic teachings. End quote.
Shaykh Abd al-Azeez ibn Abdullah Aal ash-Shaykh; Shaykh Abdullah ibn Ghadyaan; Shaykh Saalih al-Fawzaan; Shaykh Bakr Abu Zayd
Based on that, wearing green clothes is permissible but it is not Sunnah and there is no virtue in wearing them.
If wearing green clothes is a symbol for some of those who follow innovation, such as Sufi tariqas, then it is better for the Muslim not to resemble them.
And Allah knows best.