Here's why:
* Sun exposure and hair color: The sun's rays, specifically UV radiation, can lighten hair color by breaking down melanin, the pigment that gives hair its color. This is why hair can become lighter or bleached with prolonged sun exposure.
* Melanin and hair color: Black hair has a high concentration of eumelanin, the pigment responsible for dark shades. Dark brown hair has a lower concentration of eumelanin.
* Hair color change process: The sun cannot "add" eumelanin to hair. It can only break down the existing pigment.
* Other factors: Hair color is also influenced by genetics and other environmental factors.
In summary: While the sun can lighten hair, it cannot directly change black hair to dark brown.