TomCahalan
Songster
Ducklings have sex-linked color if the drake has two chocolate alleles, and the duck has none. Your ducklings don't appear to be sex-linked, and if the drake is a regular mallard, they can't be. Instead you have six that will look similar to mallards, and two that will be a lighter color. It is unlikely that they all have the same mother, because ducks will lay in each other's nests.
If your drake and/or ducks are not pure-blooded you can end up with unpredictable results.
If your drake and/or ducks are not pure-blooded you can end up with unpredictable results.