Towheaded describes someone, usually a child, with very light blonde hair that's almost white or pale yellow.

You might read about a towheaded boy running through a wheat field in a novel, or notice a towheaded toddler at the playground whose hair gleams almost white in the sunshine. Many children who are towheaded when they're young find their hair darkens as they grow older, becoming a darker shade of blonde or even light brown by the time they're teenagers.

The word specifically refers to this very pale blonde color, not just any blonde hair. Someone with golden blonde or honey-colored hair wouldn't be called towheaded. It's that distinctive, almost colorless blonde that catches people's attention and inspires writers to reach for a special word to describe it.