I recently bought a couple of repro lenses and discovered 2 things:
Thing 1 – the glass is slightly thicker than the originals which required a little fettling to get them to fit over the fixing screws. I fettled the screw heads rather than the glass.
Thing 2 – the glass is actually clear glass with an orange film on the outside. It turns out that if you cook it in French and Polish sunshine it starts to peel off. The originals are coloured glass.
On advice of the Delorean club website I have purchased this Tamiya x-26 clear orange paint – not sure whether to peel all the film off and paint the outside, or paint the inside (but see above for need for fettling).