Blue and green are the traditional colours of Jedi lightsabers. Every Jedi in the films – with the exception of Mace Windu – wields either of these two colours. Out of the two, however, blue is the more “base” colour.
For a long time (until Return of the Jedi), the traditional division between lightsaber colours used to be good = blue, evil = red. In A New Hope, lightsaber was introduced for the first time in the blue-ish form (in the original screening nearly white), and that was what the audience may have assumed to be the colour of all “Jedi swords”, until Darth Vader, the fallen Jedi, appeared with a blood-red one.
The Colour of Jedi Orthodoxy…
Blue is the colour of sky – among other things, one can perhaps associate it with Sky-walkers. It is a calm colour, in the lightsaber form it comes out as very bright. That makes it clear that we are talking about “good” colour here, leaving no room for doubt.
If we look at the way it is being used, blue is the colour of Jedi “orthodoxy”. In A New Hope, blue symbolises the Jedi tradition that now returns, but it points back to the ancient times, when Jedi were plentiful and the Galaxy was in peace and order thanks to them (or so we are told).
On the other hand, in the prequel trilogy, blue lightsabers are more often wielded by young, brash characters. It is therefore associated with some zeal. Young Obi-Wan has blue sword, as opposed to Qui-Gon’s more calm green. In the 2019 novel “Master and Apprentice”, this dynamic is nicely elaborated on when we learn that the Jedi Council assigned Obi-Wan as Qui-Gon’s Padawan exactly because they had opposing personalities. Obi-Wan used to be very much a “stick-to-the-rules” youngling, while Qui-Gon was the known rebel.
…and of Fanaticism?
Anakin switches to blue lightsaber after his defeat by Count Dooku, when he grows up to become a Knight, and becomes more focussed, more uncompromising in his worldviews. Blue can be the sort of righteous zeal that can be, under some circumstances, flipped over into fanaticism, and used by the likes of Palpatine.
From major non-movie sources, similar idea was reflected for example in Knights of the Old Republic video game. There, blue crystal was associated with the class of the Jedi Guardian: primarily a fighter, who tends to solve problems by facing his enemies head-on instead of wasting time with negotiations. Anakin turned out to be like that. And young Obi-Wan was like that, too.
In summary: the wielders of blue lightsabers usually can’t be doubted in regards to their devotion to what they believe is right. And their ideals usually are right. Peace and justice should be preserved. Anakin wanted all that, but Palpatine knew how to use these noble ideas to turn him to his side.
The unique traits of blue probably stand out the most only in comparison to other colours, especially its closest neighbour, green. Stay tuned for future parts of this lightsaber colour series.
More on lightsaber colours: