There’ll undoubtedly be some differences between hair colour percentages per nation, most especially in Europe if the maps are any indication but one wonders if there’s a linguistic dimension to it. And that certain hair colours can be ambiguous based on not only the degree of melanin but also lighting and semantics.
Among the French, their most common hair colour is what they call ‘chatain’ or when translated digitally it’s ‘light brown’. It could at least be medium or chestnut brown if we go by maps but that invites skepticism. Similarly among Germans their most common hair colours are dark blond and light brown.
They seem blonder if you include Frisians and browner if you exclude them. To be honest, from the photographs I’ve seen most Germans seem to have light brown hair. The regions with the most blond hair are central Sweden and much of Finland. Even then, especially among Swedes their most commonly reported hair colour is a dull blond.
Something like råttfärghar or practically a mousy blond colour. Like I said, it’s not just hair colour percentages but also the semantics in naming those.