Hi! Welcome to our little cookie world! 
Other may have thoughts to help, but here is what I do. First of all, I swear by Antonia74s RI recipe. Ever since I switched to that, no bleeding with black (just make sure it is completely dry). Here is the link to the recipe, if you need it:
http://www.cakecentral.com/cake_recipe-1983-Antonia74-Royal-Icing.html
One thing though about the recipe in general, she is from Canada and her MP has vanilla flavor built in whereas ours here in the states does not, so I add 1 tsp. pure van. extract during the last minute of mixing. If I need it to be white, I use ¾ tsp. instead and balance the color with Americolor Bright White.
I mix it up, going more for thick and creamy, vice fluffy. For black, I add dark cocoa (I use Hersheys Special Dark) to get it about medium brown-ish (that hint comes from SweetDreamsAT). I then add Americolor Super Black, but not as black as I will need it to be in the end as I let it sit overnight to deepen. This way you use less black coloring. Hope this helps!
I use americolor balck too - and it does get black, particularly if you color it to a dark gray and let it sit overnight to deepen. I have never gotten a true black from wilton color, though.
I used Americolor "Super Black" today and a few drops make a dark black RI. It was great! Wilton colors are not that strong. You have to start with a chocolate base and use a ton of gel.
I'll be ordering some Super Black and Super Red coloring from Americolor!! I wish I had a store near by so I wouldn't have to spend so much on the shipping & handling. I haven't had much luck with Wilton Black or their Red unless I use just about the whole bottle!! Yuk!
Thanks everyone for your advise.
Sandy
I agreee about Wilton. I had to use an entire bottle of Wilton red to color a red velvet cake and it STILL wasn't red enough. Plus you have to dig it out of the container-very messy. Now I'm a convert to Americolor. I but the large bottles to save on shipping. I should be their spokesperson!
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