This is interesting..
I was looking at the newly released official White House Obama Portrait.
On my color calibrated monitor it looked "off" with a green cast...
I saved and opened in Photoshop- here is what I can found.. (you can do this yourself to verify)
In Histogram view, The Green and Blue channels look ok.. but the RED channel shows to have been cutoff at the top.. This missing red channel highlights is not naturally occurring and looks to have been done by a post processing method..
Originally, I thought this was the result of the photographer using the flag-white to white balance the picture via the white balance tool..
However doing that would not produce the missing red channel data above. The only way I can find that produces that missing red channel highlights is by limiting the Levels Red Channel (or channels red channel) output.
You can easily verify with any picture this can be duplicated by cutting down the Red Channel Levels highlight output like this,
But there is no good reason to color correct doing that as you are throwing away highlight data and will cause other color cast problems..
If you look at the flag white areas in the background, notice the whites are DEAD on neutral-
Which indicates the photo had been manipulated via limiting the red channel output until the flag set as the white neutral.
There are two problems with this. One, is the background is lit with a different color temperature then the President (who was lit with 2 octobox strobes)
So by adjusting the entire picture for the flag white would result in the president with a green color cast (which it has)..
And second, the method of limiting the Red Channel Curve/level is not the correct way to color adjust. I'ts never good to throwaway data.
Anyway, there really is no way to properly correct this after the fact since good data has been thrown away, but i did mask out/isolate Obama and restore the red colorbalance and got this..
Just to give you an idea of what the skin tone should have looked like.
And to show them side by side.. though subtle...