The early drafts also didn't have the mentor in hiding, as such, as much as just pulled a Luke -- run away and no one knew where. As he ended up, he was definitely trying to avoid detection, so still wearing Jedi robes would not be smart.
I do wish they'd been able to leave Luke's sleeveless kimono long for ROTJ. That was such a good look. And also monastic. I feel like it's something that could have been incorporated into the story. Hopefully, talking about monastic habits won't get me smacked with the "no religion" banhammer...
In early days, monks wore whatever, and usually stuff that was donated by the peasantry, so lots of undyed, unbleached natural fiber tones or simple vegetable dyes. Off-white through brown were prominent. So some precedent there for Obi-Wan's ANH garb being something like that. But time passed and the monasteries grew in power and prestige, and traditions codified and each order identified itself with colors chosen to express the philosophy or commitment of that particular community. By the twelfth century, the habits of the orders had become distinctive uniforms. Since they'd been around and associated with the Republic for thousands of years, I expect the Jedi would have something similar in play.
We've got three broad groups out here in the real world. Benedictines were the most organized and widespread order. They eventually settled on black as their habit color and became known as "the black monks." True black robes required dye so the adoption of a processed color may have signified the relative wealth of the Benedictine communities, without refuting ideals of monastic humility and simplicity by embracing an ostentatious -- and more expensive -- color like red or blue. Cistercians follow the Rule of St. Benedict but their practices are more severe and, unlike the Benedictines, Cistercians wear undyed robes that range in hue from grayish-white to light brown. The undyed wool of their tunics and cowls is a mark of their poverty. Despite the fact that none of their garments are exactly white, Cistercians are called "white monks" to distinguish them from the more worldly Benedictines. A reform monastery of Cistercians is today known as the Trappists, who wear a stark white tunic under a black scapular to signify their strict adherence to monastic life.
Carthusians followed their own Rule, rather than that of St. Benedict, and were an order of mostly contemplative monks. They wore undyed white wool robes with white scapulars or cowls. They were also known as "white monks". People back then weren't too creative.
Dominicans wear white tunics to reflect traditional garb of teachers and represent purity. Tunics are belted in black leather and, for them, their white scapular is a blessed shield of protection from the Virgin Mary, rather than a protective apron for their robes.
Brown went in and out of fashion in general, but the Carmelites chose brown wool and stayed with it as a reminder of the cross on which ****** was crucified and of the humility of the soil of the earth. The sturdy brown robes are held together with a leather cincture, a visible sign of the vow of chastity the monks take when entering the order. The other main group who stuck with brown were the Franciscans. They embrace a life of extreme poverty and their original brown robes reflected the destitution of the peasants they served. Their robes were the ones most often made of cloth and old clothing donated by those peasants, who always wore undyed brown. The color brown also symbolizes the Franciscan commitment to protect the earth and nature and to contribute to society.
Franciscans and Dominicans are technically friars and not monks, but it all serves as a general pool of inspiration for possible approaches to how the Jedi Order might work. There could have been one single uniform. There could have been several, depending on one school of thought or another. What we ended up with is more of a chaotic mess of non-uniform-but-yes-robes. Gotta have the robes. For some reason. I feel like the Jedi needed to be identifiable by their garb, rather than their lightsabers. I also feel that they're far too trigger-happy in the Prequels. For a group with a credo of "the Force is used for knowledge and defense, never for attack", they sure are the ones to draw first in the majority of the situations we see in that trilogy.
It would have been nice if maybe Obi-Wan and Qui-Gon were "Jedi Carmelites or Franciscans" -- humble and all about service -- while the Council, when we saw them, all wore blacks and near-blacks, like the Benedictines -- being closer to the center of political power and being more worldly.
