I am going to attempt to "copy" one of the Mario cakes on this website --they are adorable and my soon to be 5 yr old really wants one for his b-day! There are a lot of black and white roads or checkered flags. How do I get the fondant such a beautiful black color? I had used black wilton gel on some fondant for my daughters b-day to make a Narnia lamppost, and it turned out more grey. How much gel for a long strip of road???
Have you tried the pre colored black fondant?
I think most would recommend just buying black fondant.
If you're making your own though, you need to start with chocolate (brown) fondant (mix in Hershey's Special Dark cocoa while preparing) and add black coloring (Americolor works well). You won't need that much and it won't be grey.
I used some purple fondant that was a deep grape/eggplant and added black to it. I had a bunch of the purple left over from a prior cake and they could not have chocolate on the cake. It worked great for me and I did not use as much black as I thought I would need. I also used wilton's but prefer americolor. (black is the web on hero cake in my pics)
Unless you need it to cover a large area, I would recommend using a gel paste and small paint brush, and simply paint the area. It will get the same desired effect w/out having to knead a bunch of fondant you might not use.
Just be certain to either allow it plenty of time to dry before applying, or paint after it's been formed/placed/molded.
Your best bet would be to start with a dark fondant. I always use the chocolate. You won't have to use so much black paste to color it. Good luck!