The yellow ducklings I have gotten have turned into fawn and white runner, pekin, and buff ducks. You usually cannot tell any markings until four weeks old or so for the fawn and white, but some you can see a slight "shadow" outlining their darker areas while still newborn.
the striped ones are usually rouen or mallard...rouen are BIG striped ones, the mallard are very tiny striped ducklings.
the black and yellow have turned out to be magpie ducks or black swedish.
the yellow and grey have turned out to be blue swedish
the black have turned out to be black runner and cayuga.
the brown one turned out to be a chocolate runner duck.
This is all that I have knowledge of...and its only from watching over the course of four months what grew into which from the "surprise mix of purebreds" I bought at my feed and seed (so, ultimately from ideal poultry).
the hatchery sites have very good pics of the baby ducklings as well as the mature ducks. I would suggest going there. It was very helpful for me!