Blond hair has very low levels of the pigment eumelanin.
Is that why it appears to light?
It is, Eumelanin is a dark pigment.
So I suppose that means that brunette hair has lots of Eumelanin. 
Correct! the lack of Eumelanin results in a yellowish color.
What does that mean for people with red or auburn colored hair? 
Some red hair involves Eumelanin but it also involves a different more reddish hair pigment. Some blond people are referred to as strawberry blond.