You were given a pretty good reason as to why your guy does not have Marans in him. Both the feathered legs and white skin of Marans are dominant features. That means that most Marans crosses will have those traits, as well.
The coloring, genetically, is a partridge type coloring. But there are lots of variations of partridge type coloring, and some breeds have different names for it, as well.
He's got a single comb (a recessive comb type), so that rules out any rose and pea combed breeds.
Single combed, yellow skinned breeds, with partridge type coloring are Partridge Rocks, Welsummers, Brown Leghorns, and Barnevelders. He could have any one of them in his mix, but there is no way to narrow down exactly which one. It's also possible that he doesn't have any of them in his background.
That's why the response has been simply 'mixed breed'.
Those were my thoughts as well. As much as I respect donrae's ability to identify breeds (probably as good as anyone at BYC), I wasn't simply parroting her. I agreed with her reasoning,