The blond-hairs / blue eyes thing is actually a gross simplification of the racial policies of Nazi Germany. They were mainly obsessed with blood purity and Japanese were seen as vastly superior to the slavs despite not having blond hairs.

A good example of this obsession for blood purity was Reinard Heydrich, a high ranking Nazi who, despite being the archetypical pure aryan in appearance (blond, ruthless and a fanatical nazi), has been the target of a smear campaign where rivals launched rumors according to which he had a Jewish ancestor, meaning he was not pure aryan.

It was a very grave accusation for a Nazi official and the Reich paid a "racial expert" to investigate closely Heydrich's genealogy to make sure the rumors were unfounded. His report showed that Heydrich had no "Jewish taint" in his blood. If the report got positive Heydrich would probably have been in trouble and could have been expelled from Nazi party.

All that to show you that it was not really about hairs or eye color but about purity and ancestry. Slavic people had a unpure blood for the Nazis and so did the jews, meaning that if you had the taint you were good for the concentration camp, whatever your eye or hair colors were.

Concerning the accusations of being unpure toward Heydrich, you can read more about these in "Hitler's hangman: The life of Heydrich" by Robert Gewarth.