Color Theory
The Lightsaber: an elegant weapon of a Jedi Knight. We all remember that moment when Luke Skywalker ignited the blue blade of his father's lightsaber. Since then, we have all wished we could have our own to battle the forces of evil. Beyond this though, there was a pattern. One we could not yet see clearly, yet it was there. One which became much clearer as the Star Wars universe expanded. Why was Luke's saber blue, then green? Why was Vader's original saber blue, then red after he turned to evil?
To answer these questions, we have to consider the concepts of good and evil, and merge them with the color wheel. In the beginning, Luke owned his father's saber, which was Blue. This was at a time when Luke knew little of the Force, and had not yet chosen his path. He was still vulnerable to the power of the dark side. This continued until the end of Empire Strike Back, when his Blue saber was lost, and he chose his path, denying Vader's offer for ultimate power. However, we could not be sure of Luke's real choice until the next movie when his saber color changes. In Return of the Jedi, Luke's newly contructed lightsaber is Green. Of course, at this time, Luke has not yet become a true Jedi Knight, and his fate is still unclear. The Green blade, however, is a clue to which path he will take. Looking at the color wheel, one may find that Red and Green are on opposite sides, and therefore opposite colors. Red is the signature color of the Sith lightsabers (Darth Vader, and Darth Maul). Naturally, the Jedi then must be the balance for the Dark Side. Those who have chosen their paths, then carry Green lightsabers. Good = Green; Evil = Red.
This can also be seen clearly in The Phantom Menace. Qui-gon Jinn, a Jedi Master carries a Green saber, while his apprentice, Obi-wan Kenobi, whose path has not yet been discovered, carries a Blue saber. Then, at the end of the movie, when Obi-wan's mentor is killed in battling Darth Maul, he happens to lose his Blue saber. Using great concentration, Obi-wan then destroys his opponent by using his master's saber... with a Green blade. His path is chosen.
This entire theory seems to fall apart, however, when one considers the fact that Obi-wan Kenobi, in his later years (A New Hope), now carries a Blue saber. This can be supported by several theories. One: he loses Qui-gon's Green saber in either Episode Two or Three and constructs a Blue one. This could symbolize many things, yet we will not discover this until those movies are released. Two: in certain martial arts, a white belt signifies beginner level, then black belt signifies Master level. However, once that Master has earned it, he/she may move onto the highest level, which is a return to the white belt. This return is based on the philosophy that the great masters enter into a state of "No Mind", therefore forgetting the knowledge they have gained throughout their experience, and being as a beginner once again *. The fact that Obi-wan carries a Blue saber at an older age could signify his return to this beginner level, even though he never openly admits to reaching a level of mastery: "I was once a Jedi Knight the same as your father." Three: some believe that George Lucas has played a trick on us all, and in fact, the old Obi-wan, is actually the real Anakin Skywalker, and the young Obi-wan is the real Darth Vader**. This would make sense as to why he picks up his master's Green saber, then carries the Blue saber later on.
Basically, it seems that the Blue symbolizes apprentice level. The next color blade then depends on the path chosen. It seems that Mr. Lucas is creating a pattern here which will not be entirely clear until the last two movies are created. Perhaps there is a greater message.
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*The concept of "No Mind"/wu-hsin/mushin can be understood when considering the manner with which a baby can concentrate with a great deal of focus and appear to be completely entranced by things that appear very simple to us. It is usually this state of mind that many martial arts masters seek to acquire.
**This theory was one that I found on a web site which I cannot remember the address of. The theory in general is that the young Obi-wan Kenobi becomes Darth Vader, and the young Anakin Skywalker becomes the old Obi-wan. For some reason, Anakin (when Young Obi-wan becomes Darth) decides to take on his former teacher's name and then become the Ben Kenobi we know in A New Hope. Of course, this does not exactly fall into the stories told in Episodes 4 through 6. Ben Kenobi's original story to Luke was that Darth Vader betrayed his father. Then in Episode 6, he came out with the truth (supposedly). According to the theory, Ben/Anakin tells Luke yet another lie, simply so he would feel compelled to face Vader/Obi-wan and bring him back to the good side, therefore, ending the Emperor's reign. In other aspects, the theory holds together: Young Obi-wan's recklessness = falling to the dark side (Vader); Anakin's good natured selflessness = kind old Ben Kenobi; Anakin the chosen one = Ben Kenobi teaching Luke which brings balance to the Force, just as prophesized; The contradiction between who Young Obi-wan's actual teacher was (Yoda, or Qui-Gon?) = Young Obi-wan's fall to the dark side and inability to teach young Anakin = Yoda becomes Anakin/Ben Kenobi's teacher. As for my personal opinion, I don't really think that Lucas would complicate the story so much. It's an interesting theory though, and I would love to see it all actually come true. It would be nice to see that good old Lucas has some more tricks up his sleeves.
...Jedi Streen
https://web.archive.org/web/20010422095044/http://212.168.23.160:80/creed/journey.shtml