We're expecting to see a lot of new things when Star Wars: The Last Jedi premieres in just over a week. We'll see new characters, new spacecraft, and new planets. However, it turns out we might see one other new thing, a new lightsaber. Director Rian Johnson is apparently hinting that The Last Jedi will include a color of lightsaber blade that we have yet to see before.
With a handful of exceptions, lightsabers have fallen into two colors throughout the Star Wars films, blue and red. The Sith, and other dark Jedi, like Darth Maul, Darth Vader, and Kylo Ren have had red blades, while the lightsabers of Obi-Wan, the young Aniken Skywalker, and most other Jedi have been blue. There have been a few exceptions, including Yoda and Luke Skywalker who went with green blades, and Mace Windu who preferred purple, but Rian Johnson implies to Parade that we could see something totally new within Star Wars: The Last Jedi.
What's not clear from this brief mention is whether Johnson is setting up a new color of lightsaber that we've never seen at all, or just one that we've never seen in the movies. Throughout the history of Star Wars, we've "seen" just about every conceivable lightsaber color, especially if you include the now non-canon "Legends" stories. If you only look at what is currently canon, however, there are still colors that we have seen before, just not in the films, including black lightsabers that were shown in the Star Wars: The Clone Wars animated series and Ashoka Tano's white lightsabers from Star Wars Rebels.
Yellow lightsabers also appear in the hands of Jedi Sentinals, though they primarily appear in the hands of characters in Bioware's Old Republic video games, they do also appear in the hands of Jedi Temple guards who are seen in Star Wars: The Clone Wars and Star Wars Rebels.
If we're talking about a lightsaber that is new to the movies only, then there's a good chance that yellow could be the color Rian Johnson is talking about. We know that Luke and Rey are on a planet where a Jedi Temple is located. While we don't expect to meet any new Jedi there, there's every possibility that the temple contains old lightsabers, and if so, they could have belonged to former temple guards and could, therefore, be yellow. Perhaps Luke, as the self-appointed new guardian of the temple, has actually traded in his green lightsaber for a yellow one?
If we're talking about a color that hasn't been seen at all within what's currently considered canon, the number of options is just short of limitless. If Rey and Luke don't find a new color of lightsaber just laying around, odds are this new color will be wielded by Supreme Leader Snoke, as the only other person in the film likely to carry one we haven't seen. If that's the case, we could something that's an off-shoot of red, perhaps a dark crimson (if we call that a different color) or something orange.