See these two reposts from athis archived Mudcat thread:

thread.cfm?threadid=98442#2023662


Subject: RE: BS: The term Afro American?
From: Mickey191 - PM
Date: 26 Apr 07 - 07:59 PM

The Black Irish I referred to were Caucasions who had dark skin & Black hair. My Father's cousin was called "Black Dick" & my Dad, who had reddish hair & fair complexion was known as "Red Dick" - both having the same last name- this appelation to distinguish one from the other....


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Subject: RE: BS: The term Afro American?
From: McGrath of Harlow - PM
Date: 26 Apr 07 - 08:20 PM

"Black Irish" in that sense generally tend to have very fair skin.   Whilst there are also a good number of Irish and Irish descended people who also have African ancestors, both in Ireland and in the Irish Diaspora.

-snip-

So Muhammad Ali (and Barack Obama) and quite a number of other Black Americans are members of both the African Diaspora and the Irish Diaspora.