My best friends mother in Mexico is almost lilly white with red hair. He’s dark skinned and black haired. Get’s it from his father.
1848 was the height of Irish emigration and during the civil war many Irish simply the United States and went to Mexico rather than being conscripted.
In fact, during the Mexican American war some 170+ Irish fought for Mexico against America.
I've got two brothers-in-law that are Mexican-American, both speak Spanish as well as English. One is lilly white, born here but parents from Mexico, they certainly can pass as white European looks. The other is brown, born in Mexico. They don't get along and detest each other.
A long time ago when I studied Spanish in college, my Spanish teacher immersed us in all things Mexican. He looked white but grew up in Mexico. Told us about a town in Mexico where practically everyone had the name Johnson (not sure, memory is failing). All white, intermarried, so the name was majority in the town. Got us laughing but he was serious.