"Blonde hair under" refers to light-colored hair that grows underneath darker hair on the head. This phenomenon occurs naturally in some individuals and can be accentuated through hair coloring techniques.
Blonde hair under has gained popularity due to its ability to create visual depth and dimension in hairstyles. It can add a subtle highlight to natural hair or create a more dramatic contrast in bleached or dyed hair. Historically, blonde hair under has been associated with youthfulness and femininity.