I am making a carved Murdoch cake, from the Thomas the Tank Engine toys, and I sculpted a face about a week ago using Wilton's rolled fondant. It was the perfect shade of grey at the time. I've left it out to dry it, and noticed yesterday that it has become green-ish. I guess the black icing color that I used has faded to this greenish color. It's too late for me to make a new face, since it won't dry in time, but does anyone have any suggestions on how I can recover? Is there some way I could paint it, or otherwise get the color right?

Thanks!

FYI, I found that if I made it a little darker to start with, it faded a little (even though it was not in any sunlight) and was OK. I guess I had started with it just a little too light.