All over South Asia - India, Pakistan, Bangladesh, Sri Lanka, from Punjab to Tamil Nadu, Gujarat to Bengal - you will find a rough correlation of class/caste along skin complexion lines with higher class/caste people generally being fairer complexioned, and a broad based folk understanding and rationalization of this. Almost every region has a complexion/caste based folk cultural model for interpreting the phenotypical variation among themselves, a variation which is often vast even over small distances - and it's independent of religion.

What you are seeing is the aftermath of thousands of years of collision of peoples who migrated from various parts of the old world with differing phenotypes. Though they all mixed, they did so in differing proportions that were correlated with the dominant power structures and associated mores of beauty, defined by the new rulers, who were frequently people of fair complexion, culminating in the situation you see today. This pre-existing situation was then keenly exploited by the last group of fair skinned rulers of foreign origin, the British.