I really wouldn't recommend that cross if you are trying to get any of the standard colors. You would have too many things going on genetically and would end up with a lot of mismarked birds. Blue in ducks is incompletely dominant. The Fawn and White is homozygous for blue (two copies) and the Blue is heterozygous for blue (one copy). All of the offspring will have at least one blue dilution gene (and show it because it is incompletely dominant). They should be 50-50 heterozygous to homozygous. The Fawn and White also carries dusky, sex-linked brown, and Runner pattern (homozygous). The Blue also carries extended black (in homozygous as well). As is the case with blue dilution- extended black and Runner pattern are also incompletely dominant.
It is very hard to cross the Runner pattern (Fawn and White, Penciled, etc...) with anything else and get decent looking birds and also to cross extended black (Black, Blue, Chocolate, etc...) birds with other colors and get decent looking birds. The sex-linked brown should not show in any of the first generation birds since it is the female that is Fawn and White (unless the Blue has it in its background in the form of Chocolate). The Black, Blue, and Runner pattern will show to some extent. Some depends also on what the Blue bird is carrying under the extended black, but you should end up with offspring that have excessive white on the heads, necks, and wings, some amount of blue overall, and probably some with showing all the preceding colors on Grey (Mallard) and/or Dusky.
As you can see, you will get quite a mix. If you breed enough offspring to cull and selectively pair a lot of the first and second generation together though, you could potentially breed several colors. It would just be a very long road filled with lots of mismarked birds.