But Y?

 For evolutionary reasons, we prefer people with good genes and high status and also we try to be like them. Lets take for example Shahrukh Khan , both genders are completely fascinated by him. Women want him for mating reasons. Women are inclined to seek men with high status and good genes (i.e. beauty or handsomeness or six pack abs are proxy for good genes). It is obvious that SRK has both the traits in extreme amounts. Men want to be like him because then they can get all the girls. As we know before British rule we lived under monarchy for a long time and hence we were ruled by kings . Also India was always agriculture-dominant society. So, Most people worked in the fields while kings and their councils reveled in the privilege and debauchery. Naturally, People working in fields became dark skinned after years of sun exposure while upper class sat in their castles and not become dark skinned. So we started to corelate light skin with privilege and high status on the other hand...