what i did was to fix fire lens onto the left side of the frame and ice lens onto the other right side of the frame...it really looks great man..anyone else did this before?
But if you look at the old transmission charts, the ones with the full spectrum graph, they still aren't equivalent in terms of the specific wavelengths they let through. Subtle, maybe, but I'd say more than enough to make wearing them an issue.
the color of the Iridium coating reflects certain light. (Blue Iridium reflects Blue light, Red reflects red, etc). That explains the slight differences in the transmission curves.
i wouldn't suggest mixing and matching lenses, even with the same colour. the degree of colour and darkness depends on batches, so i always replace lenses in pairs, never single ones.