I'm making a cake for this sunday and can never seem to get a nice dark navy color for the fondant. Could I use a blue and mix black into it? Or is there a navy blue coloring that I just can't seem to find? I usually use gel colors are those the right ones to be using?

I made some once. Started with Satin Ice royal blue ( which I think is closer to teal!) then added purple and black. Turned out pretty good.

I made navy blue fondant a couple of weeks ago. All I did was take some Wilton blue fondant and mixed in some black fondant. I mixed a little at a time until I got the color that I wanted. Easy Peasy.

i got lucky once when trying for black fondant, came out Navy Blue, i started with white MMF turned it like a purple with black icing coloring, added blue to it, and more black, trying so hard to get the darn fondant black... nope still navy blue, so try mixing some black with some blue until you get what your looking for.. My advice start out with a darker based fondant as suggested by Poohsmomma wont take near as much kneading of the color.

Americolor makes a great navy blue gel color. I purchase mine from CakesbySam.com and have been very happy with it.