If both parents have blonde hair why can their children have brown red or very dark hair?

Children can inherit hair color from a combination of genes contributed by both parents, including recessive and dominant traits. Even if both parents have blonde hair, they may carry hidden genes for darker hair colors, which can be passed down to their offspring. Additionally, genetic variation and mutations can also lead to unexpected hair colors in children. Thus, the diversity in hair color can result from the complex interplay of multiple genes.