Handsome, tall, flaxen-haired Peter Graves turns out to be a German-born Nazi spy set in among the prisoners. However, for most of the movie, you’re supposed to believe he’s a typical wholesome, red-blooded American boy from the mid-West, so I think he’s cast with that stereotype in mind rather than the Aryan ideal.
I’ve got (anecdotal) proof of this. When I was an infant, I had blond hair and blue eyes. My Polish grandmother was thrilled. “He looks like a little Polish boy!” she is said to have exclaimed. I was the only one of us four kids to have started out life that way.
When I was two, my hair started to darken, becoming the dark brown that it is today, just like my Wasp mother’s. My eyes never changed, though. What a disappointment I turned out to be!
My Great-Aunt Helen was a Polish national who had fair skin, fair hair and I don’t know what color eyes. She married a German army officer during the 1920s and moved to Germany. When Hitler came to power, her husband either divorced her or the marriage was dissolved on account of a German army officer not being able to be married to a Pole because, as the Führer pointed out in his 1924 bestseller, Slavs are basically animals. She went home to mother in Sosnowiec and was then sent to Auschwitz. I’m not sure why they singled her out, except for maybe the potential for embarrassment she carried, having been married to a German army officer. She contracted diabetes in Auschwitz and died in 1946.
Needless to say, my Slavic relatives were never sweet on Nazis, but there was a definite fondness for the blond hair and blue eyes. But even that crazy wallpaper hanger would have to admit that my Polish relatives were pretty ideal-looking for genetic garbage that needed to be exterminated for lebensraum.
There’s a point that needs to be brought up. Many Nordics are towheaded (extremely fair-haired) as children, but gain melanin with maturity, their hair becoming darker & duller. Those with red pigmentation may be luminously redhaired as children, but merely coppery as adults.
Blond and blue-eyed was the Nazi’s own stereotype for themselves. For others, Hitler was the archetypal Nazi, so he became the stereotype, to some degree. And the equation of darkness with evil probably had something to do with it.
However, I would disagree that this was a universal stereotype. There were a fair number of blond Nazis in movies, such as Wolf Kahler.