As you can clearly see in the linked articles mixed people have significantly lower serum testosterone and more importantly, lower dihydro-testosterone, otherwise known as super testosterone.
This is seen in the mixing of the once pure neanderthal European race of prehistoric times and the now african homo sapien mixed variant of today as well as mixed people in our every day life.
The Scandinavian blonde haired/red haired non brown eyed people are however the most pure neanderthal Europeans that have survived and are as a result internationally seen as the most beautiful people in the world (this also includes the most strongest too).
This is to the point whereby visually, the more pure the blondie or red hair and eyes etc the more reliably attractive the individual is likely to be by everyone else.