As a white dude, I think the fact that it's hard to isolate white culture down to a stereotype is actually one of our invisible privileges. Being the majority allows us to have all of these recognized sub-groups and cultures that are widely understood and respected. A white dude whose family is from Germany will have a very different culture than a white dude whose family is from Ireland or Spain, and that's understood and respected by other ethnicities.
On the flip side, there's a huge cultural difference between black people from the south, from the north, black people from the Caribbean, black people from Latin America (and within that, a ton of cultural variations), not to mention black people whose family only recently (within the last generation or so) left Africa. Using food as an example (the great racial uniter, if you ask me), what I experience at the Ethiopian spot I like and the soul food restaurant I like is radically different. But lots of folks (white or otherwise) will just lump everything into "black culture." Doesn't really seem fair to me. I think "black culture" is often used as a shorthand for "black inner-city culture," and even that's a huge oversimplification.
When I hear someone say, "Wow, that's super white," I usually hear that as, "Wow, that's so corny" or "Wow, that's so lame." But I guess "Wow, that's so black" or "Wow, that's so Asian" doesn't sound too good, either.
I don't fucking know - just be kind and courteous and enjoy the wonderful diversity to be found in this country.