Where does the term "red-blooded American" come from?  Why
"red-blooded," since everyone's blood is red (whether you are American
or not)?  Is this in contrast to "blue-blooded" wealthy families?

Dear hs Krustofsky (a relative of the famous Krusty?), 

The Etymology dictionary refers to "red blooded" as "vigorous,
spirited" and notes that it is recorded from 1877 (SOURCE: Etymology,
<http://www.etymonline.com/index.php?term=red>).

And indeed, the term "red blooded American" (or in other versions
found online) means an American passionate about his American-ness, a
vigorous person, first and foremost - it doesn't refer to
"aristocracy".

I hope this answers your question. Please contact me if you need any
clarification before you rate this answer.

I expect that you are right, "red-blooded" suggesting an active,
aggressive, "spirited, strong" person, versus the presumed effete
character of a nobleman.

Interestingly, I found this definition of the latter on etymonline.com:
"blue blood Look up blue blood at Dictionary.com
    1834, translating Sp. sangre azul, claimed by certain families of
Castile as uncontaminated by Moorish or Jewish admixture, probably
from the notion of the visible veins of people of fair complexion."

Perhaps our British friends here can comment on whether "red-blooded"
is limited to describing Americans.