[pjd]

Here in Michigan, a Black Cow was Coke and ice cream, in a blender. With root beer, it was called a Brown Cow. With Vernors, it was called a Boston Cooler (even though they didn’t know what Vernors was in Boston.)

[Red Badger]

This is the only 'Black Cow' I ever knew of:

[John Milner]

I remember black cow being with cola instead of root beer.

The one with root beer was just a root beer float.