Coralline Algae does vary in colour, with deep purples, light pinks and reds. I have never seen any green though. Is that what you have? When corralline does off, it can be covered with other forms of algae, giving it a green colour.
hmmm well just think back to when you bought it if the algae thats in the same area was the normal color its possible it dies and like mr. miagi said something grew on top of it or covered it, but thats on new live rock so im not sure
nah this is new hard alge that grows in circular patterns .. the glass cleaner wont take it off i have to manualy scrape it with a razor blade. will post a pic in a bit.