Colorism predates the modern era in nearly all cultures.
During the Elizabethan era England, women used Venetian Ceruse, a mixture of white lead and vinegar, to paint their faces and necks chalk-white even though it caused hair loss, skin corrosion, and muscle paralysis.
In the early phases of globalization and during the great divergence, white/Western societies began to see themselves as the nobles of the world and their colonies as the inferior laborers. Essentially, it is what you're describing but on a global scale. This further entrenched colorism globally.
Reversals of this mindset have only happened in the past 75 years.
The nature of endogamy is such that, in my experience, the first preference is that their family member marries someone of a similar South Asian background and social standing. Marrying someone Indian outside of those bounds is the next preference and then marrying someone non Indian. In all of these categories colorism is at play.
Think of medieval clans using marriage to form ties or to consolidate wealth and influence via marriage. Marriage is seen almost as utilitarian with individual wants and needs set aside for the collective.
It's an ancient way of thinking and I don't doubt for a second that it'll be eradicated with time as it has been in many parts of the world that successfully defeudalized who did not have to deal with foreign occupants further entrenching a feudalistic mindset.