I have a charcoal suit and love it. I also have a black one. I do not have a dark navy suit, and don't really care to go buy one.
I know of more than one person who's been hired at Delta that didn't have a dark navy blue suit with a solid red tie. Everyone gets hung up on the color of the suit for interviews.
Buy a suit that you love, have it tailored, get a nice tie that goes well with the suit and whatever dress shirt you like and get a nice pair of shoes. As long as you look good (aka: you look like you're worth $1millin) it's not going to matter in the end.