Your age is not mentioned.
Skin color is due primarily to the presence of a pigment called Melanin
, which is controlled by atleast six Genes.
People with light complexioned skin mostly produce Pheomelanin, while those with dark colored skin mostly produce Eumelanin.
Nature has selected for people with darker skin in trapical lattitude, especially in nonforested regions.
Try this , but not sure to get white skin.,
Avoid hot sun light during noon hours.
Apply sandalwood powder with rose water mix all over body.
Take pure safforen with milk at night daily.