If blond hair is a recessive trait, why are there so many blonds? What makes it recessive?

Recessive traits are usually linked to a *lack* of expression of gene product responsible for making the dominant trait. That is, the body makes less stuff that would make you look like someone showing the dominant trait.

In this case, the gene product is a protein or set of proteins responsible for putting together melanin. Melanin is the pigment that gives hair its dark color. If you have two recessive alleles (or copies of a certain variation on a gene) of a gene responsible for these melanin-generating proteins, you will get lighter skin, hair, and a tendency to have a more blue eye coloration because you make less melanin.

Keep in mind that heterozygotes are organisms with BOTH the dominant allele and the recessive allele, even though they may appear to have the same hair color as people homozygous for the dominant allele (that is, having two copies of the dominant allele). This is because the one copy of the gene that they do have makes melanin successfully, just enough to give the brown coloration- though they probably don't make as much melanin as their homozygous dominant cousins.

What this means is that when two people who are heterozygous have children, those children may be homozygous for the recessive allele even though their parents may both have had brown hair. For the same reason, their children may have blue eyes even if their parents both had brown eyes. This is why you can have as many natural blondes as you do (where, exactly?) running around, even though the trait is recessive.

EDIT: Why might these alleles cause a lack of melanin expression? It's because the mutations in the genes either change the proteins responsible for making melanin such that their activity is either reduced or inactivated, or they change proteins that are involved in the interaction networks that activate the expression process (e.g. transcription factors are mutated; receptor proteins lose affinity for signals to begin the process, etc.).

Many genes contribute to hair and eye color; the recessive alleles are often single-nucleotide polymorphisms (changes in single nucleotide bases) that can cause just one amino acid to change. There may be more drastic changes to the gene such as deletions, insertions, and inversions that cause different effects, but I am not aware of these in the context of eye color.

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If blond hair is a recessive trait, why are there so many blonds? What makes it recessive?

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