I agree with the general consensus, there is no "white" culture per se, uness you're talking about the bad craziness of nationalism.
What I think OP means is "plain vanilla American culture." And that's the thing. The US is so huge, so comparatively young as a nation, that it's hard to even have a culture.
Furthermore, anywhere you go in the states, you have pretty much the same TV, same radio from central locations, news anchors from the same school, holding the same rip 'n' read newscast. The corporate world has skin in this game. Keep us homogenized and you keep us focused on the consumer culture they want us to have.
That said, we Americans who don't identify with any ethnicity do have cultures, but it's based more in what we do. Bikers, goths, snowboarders, rail fans, Trekkies, and then some. Those are all cultures.
Then too, when we try to do culture, because of our media obsession, it often becomes a parody. Case in point, I once went to an Oktoberfest here in California. I saw people wearing stereotypical "German" costume, playing a Polish-American wedding game (Chicken Dance) and singing an Italian children's song (Rooki-Zooki). That's about as all-American as it gets.
Everyone knows birds aren't real!