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.
That is very interesting! So Strawberry Blond people must have small amounts of Eumelanin but also the other pigment.
Red hair
Red hair (or ginger hair) occurs naturally in one to two percent of the human population, appearing with greater frequency (two to six percent) among people of Northern or Northwestern European ancestry and lesser frequency in other populations. It is most common in individuals homozygous for a recessive allele on chromosome 16 that produces an altered version of the MC1R protein.
Red hair varies in hue from a deep burgundy or bright copper (auburn) to burnt orange or red-orange to and strawberry blond. Characterized
Blond
Blond or fair hair is a hair color characterized by low levels of the dark pigment eumelanin. The resultant visible hue depends on various factors, but always has some yellowish color. The color can be from the very pale blond (caused by a patchy, scarce distribution of pigment) to reddish "strawberry" blond or golden-brownish ("sandy") blond colors (the latter with more eumelanin). Because hair color tends to darken with age, natural blond hair is generally rare in adulthood. Naturally