What component inside a lightsaber determines the color of the blade?

• the primary crystal
  According to non-canonical sources -- books, comics and other media -- the primary crystal inside a lightsaber determines its colors. Dark Jedi and Sith tend to use synthetic crystals, which give off an ominous red glow.
• the energy modulation circuits
  According to non-canonical sources -- books, comics and other media -- the primary crystal inside a lightsaber determines its colors. Dark Jedi and Sith tend to use synthetic crystals, which give off an ominous red glow.
• the midichlorian chamber
  According to non-canonical sources -- books, comics and other media -- the primary crystal inside a lightsaber determines its colors. Dark Jedi and Sith tend to use synthetic crystals, which give off an ominous red glow.