Interesting subject Ben; well done.
We don't use any artificial UV in the form of lighting on any of our reptiles;
mostly due to the over all expense.
I do believe however; 'natural sunlight' aids in both the colour and over all
health; and appearance of any animal....
Will we ever really know just how beneficial it is?; probably not.
Over the years; while working with different types of wildlife;
I've noticed regular exposure to natural UV;
does in fact; seem beneficial in enhancing the colour; especially, in birds and reptiles.
It also seems to aid in the recovery of sick and injured animals from what i've experienced.
I'm sure most of you have seen your dog; go and lay out in the sun when it's crook.
Due to overall numbers these days; we don't do it nearly as much as i'd like.
We would often; put most of our juvenile herps into a outside sunning enclosure on a regular basis...
Most notably; we have observed a remarkable increase in the general over all colour of young snakes, and monitors;
that regularly have these 'sunning' sessions; as low as a few hours a week...Bredli, jungles, children's etc; to name a few.
Aside from colour; these juveniles seem to always become better feeders...IMO
The animals also tend to become quieter; probably due to having a set routine; and being handled on more of a regular basis.
A simple 'steel fly wire' type enclosure; complete with a few rocks, branchs, potted plants etc; is all thats needed.
Try; for example; regularly sunning a washed out old jungle; you may be surprised; just how much brighter it may become...