Lightsaber colors are an important part of Luke Skywalker a green lightsaber to use. That opened the door to a whole new world for fans.
Various lightsaber colors appeared in the Star Wars Expanded Universe, but it wasn't until the prequel trilogy released that audiences saw a brand-new color for the first time on-screen (and in canon): Mace Windu's purple lightsaber. It's widely known that Samuel L. Jackson requested the purple lightsaber, and Lucas abided. There wasn't a plan for it to be included since the common lightsaber colors at the time were blue and green for the Jedi and red for the Sith. Later, though, a black lightsaber was introduced into Star Wars canon.
Star Wars' first black lightsaber, Star Wars: The Clone Wars season 2 in the Mandalorian story arc. It was a sword-esque weapon that emitted a white glow on the outside; the original plan was for its , Pre Vizsla, to use a vibroblade, but according to Dave Filoni (via IGN), George Lucas didn't believe a vibroblade would be able to combat a lightsaber, so they changed it to be a black lightsaber, modifying its design only slightly. Since it was a unique circumstance, Lucasfilm never made another black lightsaber.
In-universe, Tarre Vizsla was the first and only Mandalorian Jedi, and like every other Jedi in history, he needed to construct his own lightsaber by finding a kyber crystal that represented himself. That crystal ended up forging a black lightsaber. In Star Wars, people can't merely go searching for a kyber crystal and come back with whatever color they want; the kyber crystals have to be attuned to the Force-. It's just that no one else has been able to create a black lightsaber before or since Tarre Vizsla existed over a thousand years before the original trilogy.
Today, the Darksaber is a unique weapon in Star Wars lore that has finally been adapted into live-action. After appearing in various episodes throughout Clone Wars and Star Wars Rebels, the Darksaber was used by Moff Gideon in yellow in Star Wars: The Rise of Skywalker (though yellow has been used elsewhere by temple guards) - the one and only black lightsaber remains the Darksaber.
