What Causes Difference In Skin Color Of Face And Body In Kid?

hi doctar,my baby is now 5 month old .there is lot of diffrence in colour of her face and body .Her face ,neck ,hands and feet are very fair as compare to her other body.what could be the reason .can we do anything .one more thing now can i start ubtan(besan pack)or shd i wait more.tks in advance regards