I got that by encasing the quote in color=lime tags, as can be seen. I clicked Preview, to see if "Lime" was a supported choice, and ended up coloring my sig. The color did not show up when I posted the reply. Also, when I went back to edit in my commentary, I forgot to remove the color tags, and, even though the tag was closed after the quote, it still managed to color my words lime.
Not exactly forum-shattering, but an interesting bug regardless.