Why does our skin gets dark in colour when we stay in extreme sunlight for a long time?

Kindly refer to the link below:-

https://www.meritnation.com/ask-answer/question/what-is-the-importance-of-melanin/control-and-coordination/10547943

To prevent the skin from harmful radiation from sunlight melanin comes on the surface of skin thus protecting it from harmful radiation.

Regards