The Brown Scapular (our Lady of Carmel) was first promoted by St. Simon Stock (England) around the 1200’s. The Green was first promoted in France 1700’s. Both are devotions approved by the Church, for different purposes.
The Brown Scapular, and being invested in it makes one a member of the Carmelite family. Wearing the Scapular is the least of the responsibilites that one takes on with enrollment. One should be ready to devote time in each day to prayer. Typically this means reciting the Little Office of the Blessed Virgin, although a confessor can commute this to reciting the 15 decades of the Rosary or other suitable prayers. If one is a priest or religious, the Office of the day suffices. Fast and abstinence on Wednesday and Friday, is also included, although that to can be substituted with another penitential action which one’s confessor can permit. There are a few other conditions, such as frequent confession and worthy reception of Holy Communion, and prayers for the Holy Father and the Church. Once one has been invested in the Brown Scapular, any replacement brown scapulars, or the scapular medal need not be blessed when the original wears out, just worn in place of the original.
What Jon says is true, thinking that just wearing a cloth scapular means that you will go straight to heaven, no stopping over in purgatory, or need to live a holy life is hocus pocus. Many Anti-Catholics, and uninformed Catholics are unaware of the conditions for the proper use of the brown scapular. The Church has granted special graces to those who fulfil the requirements of the scapular, and live a life striving for holiness.
The Third Order of St. Frances has a scapular and cord, that members wear. So too the Servite Scapular, and the Norbertine, as well as other third order members.
The Green scapular is not like the others, it does not require blessing, and it’s devotion is intended to ask our Lady to soften the hearts of those who are lacking in graces to see the truth of the Catholic Faith.