Duffy Genetics - Where did the dark colors go?

In a previous post, I touched on the perplexing concept of Duffy's having dark skin and dark hair, which seems to have been totally lost by my generation.

I found photos hidden away of John James Duffy and Bridget Helena Murphy which may give clues to what happened to the dark skin and dark hair that traditionally belongs to the Duffy clan.

Bridget Helena Murphy and John James Duffy
Iowa City, Iowa

 I am assuming that this photo was taken around the time they were married (1894).  It appears in this photo that Bridget has fair skin and I have another photo where her eyes appear to be light-colored.  In an earlier post, I said that three of Bridget and John's children had fair-colored skin, but I didn't know about that other two as they had died young.  Now a picture has surfaced of young Willie.  As best as I can tell from this photo, he has very pale skin and light-colored eyes.

Willie Duffy
Williamsburg, Iowa

John and Bridget's firstborn, Michael, apparently died on the day he was born.  But from what we can see, the Murphy light-colored genes drowned out the Duffy dark-colored genes in this generation.  And with the next generation, the Kelly genes are mixed in with their red hair and light skin, and the dark is completely gone.