You have a customer caring skills more than their skin beauty. Because the passengers wants more care rather than your skin beauty.
Is it compulsory to have fair skin tone to be an airhostess?
It is compulsory to be physically fit, take self defense classes and be firearms rated while having mandatory basic life saving course under their belt. Beauty has little to do with being a airhostess except maybe on what's his faces jets for virgin atlantic. In other words it doesn't help a bit to have looks if you can't do the job. But I would say basic appearance/hygiene is necessary (to look good in your uniform). Be a nice/kind hostess in all situations.
They have several prerequisites and requirements but fair skin is not one of them. So if you are reasonably smart, well informed and carry yourself well, you have a good chance to be grabbed by any airlines!
To become an air hostess height is compulsory and communication skills - English and Hindi language.
I guess you haven't flown on an airplane very often have you? Most of them do not have white skin.