White isn't a dominant colour in Runners?

[GrannySue]

I had been taught that a white drake bred to a mixed colour duck would almost always produce a white duckling.

That doesn't seem to be the case for me. Both my drakes are white - one from a long line of show quality birds and the other who is either his son or his nephew. I guess the father of this little cutie must have been the younger drake, whose mother is one of a variety (non SQ) of colours.

 

[Sweetfolly]

Nope - in ducks, white is recessive. A duckling would need to get a copy of the gene from both parents in order to hatch out white.

Here's a good page on Indian Runner duck color genetics: http://www.luckyhit.net/ducks01.htm
Here's a little blurb on White genetics from that site:
Recessive white, "c," is recessive and responsible for the white in common white breeds. In the homozygous state (c,c), recessive white masks all other color genes.

Therefore, white ducks also carry color and pattern genetics, but the expression of those colors and patterns is masked by the white gene "c".

That duckling sure is cute though! Looks like you have a little Pencilled Runner!