Strangely enough after fluffing out it almost has the faint markings around it's eye and on this back like a Rouen would.. should be interesting to see what it grows up to be..
Your baby looks like a "buff", but that would require both of the parents to have donated a recessive "dusky" gene, which may not show in either parent, since it is recessive.
And a blue-dilution gene, which your Saxony has, but would also show up in the mom if she had it.
And a sex-linked brown dilution gene, which could have come from the Saxony, where it could have been a hidden recessive gene. Or if it came from momma duck it would have shown in her coloring.
And those pekins in the photo with her? Could they have been involved? Sperm from a male duck can live in a female for up to 3 weeks. I've even heard of cases as long as 6 weeks. Are you sure she wasn't with ANY other ducks for at least 2 1/2 months before this baby hatched?
Your hen doesn't have any blue or brown dilution, so your baby is not a buff.
There are a lot of colors that look alike as ducklings, but they can change as the bird grows.
Keep us posted. It'll be interesting to see how he feathers out.