Madigan's have always been white legged fowl to my knowledge, possibly a few yellow legged fowl. They are the same blood as the Claret's from Madigan which are mostly white legged fowl by the ones I've seen.
It mentions at one point "A grey Claret cock bred to a Herrisford Brown Red Black and Tan hen in 1922 was the source of the dark legs in many of the greys." But really, I figure it matters very little now. Finding "pure Madigan greys" would be very unlikely I imagine due to people crossing so much and many breeders may say they have something pure; agree to sell you said thing, and in turn give you something they may not even know the breeding of because they bought it from someone else to sell as their own.
I've heard plenty of stories of even big name breeders that charge big money to know it is true. A lot of the "Stewart Yellow Legged Hatch" you see for example probably do not carry much or any Stewart blood. I've seen a great deal which looked like Sweaters to me and not like the Stewarts that we had (still have one cock) at all.
The reason for that would be one of the main suppliers would be a known feather peddler in these parts; but to the people that buy them it isn't known.