Nope...bill color isn't going to tell you much. Sometimes bean color on khakis can be a clue, but I don't know if it is consistent. Read the sticky for more clues or vent sexing info. I have had ducks for over a year and still don't know how to vent sex. I am too afraid of hurting the ducklings.
There is a sticky at the top of the duck forum that gives a lot of details, but basically, you will have to wait a few weeks. If it is LOUD and quacks, it is a girl. If it makes a raspy peep noise, it is a boy. Eventually the boys get a curly drake feather, but your first indication is usually...