Another reason seems to me is, people misuse certificates, and that also might be the reason that medical certificates issuance has been stooped (Medical certificate, and on its basis, NOC can be easy to get, and to curb it, they have stopped issuing them).
So, as per current rules and as per my limited knowledge, no sort of tint is legal and allowed for general public, nor are Windows shades, blinds, etc.
Whether one likes it or not, has skin issues or otherwise, a rule is a rule; a person must accept it and it must be obeyed and followed.
I hope, this all helps. Thank you.