(This post is from an email conversation with two friends. I thought the content might be useful for others.)
Q: Anybody know what’s causing the black outfits to show their true colors? To the eye, of course, these were simply black outfits. All four images are taken with my Nikon D200, although I saw similar variations on my D70. The top two were intentionally underexposed — as measured by the camera’s meter (which always want to overexpose in these kinds of situations, which would blow out the faces). And the top two were both shot with a 50mm f/1.4 lens whereas the bottom two were shot with a 70-200mm f/2.8 lens. Could it be coating on the lens? Photoshop CS3 interpreted them the same way Aperture did, so I really think it’s in the image data.
A: Well, I would suggest that in our normal experience, there is no such thing as black, only shades of very dark shades of gray. (I’ll not contemplate the philosophical implications with which I’m sure I disagree…) And therefore anything dark we normally come across, with enough exposure, will become lighter and even white. And whenever it gets enough exposure not to appear black, then it will possibly become non-neutral. My wife is always asking me if her black shirt and pants “match”, and sometimes they don’t, but it really depends upon the light as to whether or not it’s evident. This issue is similar to what causes metamerism (http://en.wikipedia.org/wiki/Metamerism_(color)) in B/W prints printed on most inkjet printers.
I can’t tell if the lighting is typical colored (RGB or RGBY) stage lighting. If it was, then that will emphasize the colors of “neutral” fabrics even more. All of this, plus the fact that different lighting has varying amounts of UV and IR light that we don’t necessarily see directly but that sometimes will be visible when reflected from stuff and that definitely will be picked up by digital camera sensors.
I doubt that the cause is due to the use of different Nikon lenses. Nikon says about their SIC (Super Integrated Coating) that it is intended to maintain a “uniform color balance that characterizes Nikkor lenses.” I’ve never noticed any particular Nikon brand lens having a color cast different from the rest. (http://www.nikonimaging.com/global/products/lens/glossary.htm)
Most folk wouldn’t know to intentionally underexpose a dark subject and likely would have seen the issue even more than you did.