After a brief search, I found at least 15 instances of a yellow lightsaber in legends, from various eras, old republic new jedi order, prequel era, etc. That’s only counting yellow and not green-yellow, like Ahsoka’s in TCW, or orange or any other variant found elsewhere in legends. They didn’t appear in the OT or the prequel films, but they have appeared from time to time in canon comics, high republic stuff and in rebels.
In legends, there were some different meanings, as the post above said, that were assigned to different colors, but in canon, the most robust meaning to the colors from what I remember, is that red sabers are red because the crystal has been ‘bled’, and (correct me if I’m wrong) white sabers are made with red crystals which have been ‘purified’ or healed. As for the other colors, in canon it seems that they are specific to how the crystal responds to the person who uses it to make their saber, but as for specific meanings to blue, green and other colors, I think maybe we just have to use our imagination. I don’t think it’s of particular significance, but colors do tend to shape our perception, hence why the bad guys have red in the first place, so maybe yellow is significant in some other way idk. I think it suits Yord.