Superman ice cream is a Michigan thing involving three flavors (in shades of blue, red, and yellow—your standard Superman colors) working together, sort of like Neapolitan. So is it just vanilla ice cream with buckets of food coloring? Apparently no, at least not in the case of the blue flavor. Blue Moon, another Michigan (or maybe more Midwestern in general) thing—and not beer in this context— is a super sweet Smurf-colored flavor that apparently "just tastes like blue." Some guesstimate that the yellow is vanilla (others have said banana, but they have little support) and that red is cherry, raspberry, strawberry, or another generic sweet-ish red fruit.
It sounds like a bubble gum ice cream situation—you start hitting puberty, and it becomes less cool to have blue lips; suddenly pralines 'n cream is the more sophisticated option. But grown-ups eventually come back to it.
Like MGEats, a native Michigander who is headed to New York City and has a craving. Sadly, we haven't located a source yet, but maybe if more of the world knew what Superman ice cream was, it'd be more findable.