We had all blues, then one sat on the nest and hatched out 14 babies! I don't know how the mother duck covered them all! Actually, she had 17 eggs but one was never fertile and others died around hatch time or a little later. But of the surviving, there was the splash (basically mixed colors), the silver, five blacks, and the rest were blue.
I think, if you breed two blues together, you are supposed to get around: 50% blue, 25% black, and 25% mixed silver or splash.
If you breed two blacks together, you get all black.
If you breed silvers and/or splashes together, I'm not sure what you would get. There's not a lot of info on them compared to blue or black, which is why I started this thread.
The other colors are apparently really rare recessive genes. Look up "chocolate swedish" here on the forums, and you'll find a thread with a pic of a chocolate duckling. It's really cute.