The difference between a green lightsaber and a blue lightsaber primarily lies in their color. In the Star Wars universe, lightsabers are constructed by Jedi and Sith using kyber crystals, which determine the color of the blade.
Blue lightsabers are commonly associated with Jedi Knights and symbolize peace, justice, and protection. Some notable Jedi who wielded blue lightsabers include Anakin Skywalker and his son, Luke Skywalker. Obi-Wan Kenobi and Yoda also wielded blue lightsabers in the prequel trilogy.
On the other hand, green lightsabers are typically associated with Jedi who have achieved a higher level of mastery in the Force. Green is often seen as a symbol of growth, harmony, and wisdom. Jedi such as Yoda, Qui-Gon Jinn, and Luke Skywalker (in Return of the Jedi) have been depicted using green lightsabers.
In terms of functionality, there is no significant difference between a green and a blue lightsaber. Both colors indicate a Jedi's affiliation with the light side of the Force and their skill in lightsaber combat. The choice of color often comes down to personal preference or the specific narrative choices made by the filmmakers.