You cannot change your skin color. Wherever we live affects our physical aspects surprisingly. If you lived in Hawaii, your skin would always be plump(because of the constant moisture) and there would be nothing you could do about it. On the other hand, if you lived in Nigeria, you would be constantly exposed to a hot climate, therefore affecting your skin color. Genetics also play a role, so your skin has already been predefined. However, if you want to improve your skin, drink lots of water, as it will clean the toxins beneath your pores and enrich your internal oxygen.