I think it's because Nikon are very careful to organise their colour for skin tones. The result of this is that I've had continual difficulty with landscape in the early morning and evening (too much yellow is usually the problem). Abandoning AutoWhiteBalance and settling for Daylight did help, but still I was always fiddling about with the colour and being dissatisfied.
Both the A900 and the M8 produce colour which is 'satisfactory' (i.e. I accept it, or even like it). I've sold 3 sets of Nikon gear on the basis that I was unsatisfied with the colour . . . and then bought back in again . . . and then been dissatisfied again. I won't do it again.
Jono
A couple of thoughts regarding Nikon color especially D3 images, which hopefully will be helpful. Will try and make this brief as possible for now but can elaborate later if required or needed.
You did not say which converter you use for your D3, which will make a difference though at least in my experience nothing that is insurmountable. There are those who claim only NX or NX2 will give reliable and decent conversions for their Nikon cameras, I am not one of those and prefer instead the LR/ACR conversions.
For what ever reason NX sees color differently from other software, or perhaps it could be said the other way around ACR/LR et al see color differently than NX. Regardless, when using a custom WB via the custom WB pre-sets color accuracy will increase substantially. So if you are using lets say the daylight pre-set for your landscapes while using ACR for your conversions and given that ACR sees color differently than NX/NX2, then most assuredly you are not getting an accurate let alone the best initial conversion possible. With auto WB it could be anywhere and most likely worse still. Curiously ACR/LR and perhaps all of the other converters as well disregard Nikon in camera settings regarding color, contrast etc except one, that being the "custom" pre-set WB. You can store up to four of these custom pre-sets permanently and a 5th setting that is ever changing as needed.
I use a Whilbal gray card to set daylight color (in order to simulate a roll of daylight film, say around mid morning) for a given batch of lenses like the newer nano crystal coated ones and will have other stored pre-sets for some older lenses like my 80-200 F2.8 which does render color differently than the newer glass. As a rule I don't bother to implement a custom WB for other times of day, otherwise you might kill some juicy sunset colors, and yet another reason to be cautious about using Auto WB. Hope this makes sense. Likewise I do the same for my in studio settings and lighting for a given setup. By now I have photographed hundreds of paintings, which really do require accurate color, using this method with excellent results and only minor tweaks in PP. In any case I don't find Nikons to have a predilection toward flesh tones, vs landscape color or any other situation. Its all a matter of how one goes about their custom white balances, IMHO.
Hope this helps.
Rob