Blue is not the only color crystal Cal can use in Jedi: Fallen Order. There are a handful of colors he’s going to discover during his journey, but to get to them requires you to progress through the game to a certain point.
During Cal’s journey, you’re going to find yourself visiting the planet Ilum. It’s where many of the Jedi visited to receive their kyber crystals, which they bond with through the force and go into their lightsabers. These crystals powered the Jedi’s weapon, providing their unique colors.
When Cal arrives at the moment of truth to choose his lightsaber color, he can choose a new crystal and has several options available.
You get to choose from the eight options. Blue and green are available from the start. If you pre-ordered the game, you get orange immediately, too, alongside green and blue. However, when you return to the Mantis, all of the colors are going to be available to you.