When people can look at the finished photos and identify the brand of camera they were shot with, WITHOUT that brand information being given to them or otherwise discerned via EXIF or any other means, then it will be a question worth asking.
You actually can, greens appear very differently between Nikon and Canon. It's not hard to spot on unedited images between the higher end models.
Smells like a giant load of BS to me.
1st, who would be showing unedited "FINISHED" images, especially if they're using a higher end model?
2nd, how would you know what hue and luminosity the real-life green was to begin with, in order to discern what the camera may have done to it, let alone what post processing may have done to it?
Back to reality: Show me the people who look at random images printed or online who can pick out the Nikons from the Canons just by viewing the photos.
1st off I'm in no way saying that the difference is important or even very noticable.. Just that it is discernible.
1. Well, noone in their right mind, and that's why it doesn't really matter.
2. For anyone who wants to know, all that matters to discern the difference is that the tone of the green in two identical images from a Nikon and a Canon tends to appear darker and more subdued from the Canon (I could have this mixed up it may be the other way around) This is a very slight variation but will appear time and time again if you reproduce the experiment.
So, it is nearly impossible to tell once the image has been processed, but the difference is still a fairly important factor as it is comparable to the differences of color reproduction on film.. The aesthetic of each camera may work better for different sorts of shots, and the RAW data from the greens can slightly affect the way you can process the image. (But in a negligable amount)
So you're right, post processing basically makes that whole variation of color a mute point.
I'd also like to correct myself.. I said they appear very differently, I was being dramatic, they only look slightly different.
I just wanted to throw one technical difference between the two cameras in here.