I believe what was meant by provide a solution is “write shader code to do this”. If you can not, you have absolutely 0 right to say anything is “simple”, otherwise you should just go do it.
Oh and regarding the glass, that’s hardly a tinted car window.
it works slightly differently with blown glass, but the idea is the same. You pigment silica with different colors/dies. Just because melting it makes it appear as one surface it does not mean you have just one surface.
and you may or may not use coatings on blown glass too. It depends on what kind of finish gets put on it, so you should probably refrain from generalizing it in the first place.