It's an obvious matter that some lenses render colours in a less saturated manner than others: old uncoated lenses, for example, not always give as rich colours as modern multicoated ones.

But is it because such lenses increase colour saturation (e.g. by selectively letting certain wavelength corresponding to primary colours go through more easily) or because they avoid the problems, such as flare, that desaturate colours?

I'm suspecting coating and glass type have a lot to do here with the avoidance of problems, in that they reduce parasitic light due to internal reflections, but I wonder if there are other variables at play.