I know that I have had some odd color sputum from time to time, but it's usually related to something I had exposed myself to - some thing with a lot of dust to it.
I did find these links, although I don't know the reliability of their information:
www.newhealthguide.org/Black-Mucus.htmlwww.healthhype.com/sputum-color-causes-and-meaning.html