The idea that "non-Hispanic white american" is not a distinct ethnic identity (usually just "White American" or even "American", with Hispanics viewed as non-White , actual ancestry aside, outside of bureaucratic systems and foreign in ethnicity) despite recognition of distinct national origin, is somewhat dubious. Its true that some of those national origins historically were viewed more as distinct ethnicities and even treated as just as non-"White American" as Blacks (or, perhaps more germane to the point, White Hispanics) are now, but while the national identities persist, that treatment has largely changed. I mean, sure there is a time when by virtue of his mere name Bill O'Reilly would be a reviled enemy of the nativist defenders of White American identity, rather than in a position to be an icon of nativism. But that time is long past.
I get that white in the US means a lot of different things, but it's not like Spain or Germany are a homogenous glob.
France and UK are as different as France-USA, UK-USA. Europe is extremely diverse across borders.
So, the 75% of America that is 'Ethnically European' is already very varied.
Also - a good chunk of the 'non-Norwegians' in Norway are Swedes and Danes, which are pretty close.
Maybe genetically (although even that is debatable). But after a few generations you kind of iron out the differences between, say, a German - American and a Polish - American.
The differences between Germans and Polish are much larger. They speak German and Polish for instance vs just English.
Also when you are saying colonies, is it the former colonies (North Africa, Sub-Saharan Africa, Ex-Indochina) or the current overseas departments (in the Carribean, Guiana in South America and in the Indian Ocean)?
Yes, Norway is fairly homogeneous. But most countries are fairly homogeneous, Norway doesn't really stand out.