You didn't read the Visual Dictionary closely enough. The electrum in his saber is the saber's gold-colored finish. "For Council senior only".
Sith crystals are synthesized; engineered to make a very slightly stronger blade when given dark energy from the user. Since Jedi crystals aren't, we have to assume that means blue and green producing crystals are the most common. However, obviously not all natural crystals are blue or green---observe Mace Windu's vibrant purple