In the south, it means looking fairer. There is inherent racism basis skin tone. It is not just how you look though, it is your name which can have case based surname or a first name variant common to a caste. Eating habits, how you speak the language - dialect and kind of words you use and so on.

Not just in South India, although the pattern is perhaps more distinctively visible there.

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.

Would it be similar to how a British person might recognize a posh individual?

Yes.

Yes there is a difference in South India. The Brahmins are descendants from central Asia[1]. But this is often refuted by the Brahmins in India as they claim to be from an authentic Indian origin. The natives in South India which includes me are darker skinned than the Brahmins. So people here can figure out that someone is from a caste if they are light skinned. A person with proper scientific understanding can explain in more detail but this is the overall view.

[1] https://economictimes.indiatimes.com/news/science/steppe-mig...

why should David Reich be trusted more than David Frawley ?

Not completely dark + looking dorky I think? I make it a point to ask why they thought I was one but no one ever has an answer.

Brahmins generally have lighter skin tone. I am guessing this is because they usually marry people lighter skin tone. There is probably some inbreeding too historically and even now https://pubmed.ncbi.nlm.nih.gov/950239/

Frappuccino skin, long and slender bone structure. And yes, a bit dorky.