The D800 has so much dynamic range though that contrast, saturation, and tonal scale are very malleable in post. Once process adjustments are done there is still some remaining difference in color, with the Leica picking up green-blues more strongly (as is pretty typical for Leica glass) - dark blues appearing almost luminescent - but apart from that which is a pretty subjective preference, there's not a whole lot of difference.
But yeah, Zeiss glass calls for lightening shadows a little in post IMO. But so do the top-shelf Nikons...
Its not as simple as fixing things in post ..but there are two dimensions to consider . When I had the D3x and the DMR ...I could test both R glass and nikkor primes on the Nikon sensor and then compare to the DMR with R glass . Both the sensor and the lens affect the resolution,contrast,saturation and tone separation (as does post processing).
The DMR had better color ....cleaner separation of the colors and a real depth that was not present with the Nikon . (it had a lot of others issues ..but the DMR had great color ).
So move to the Nikon ...with the R glass you could see the character which I described above . To my taste (and thats clearly subjective) the R glass was pretty great . The Nikon glass was a mixed situation ...the newer nano coated primes and even the new 70-200/2.8 were big improvements .
Its in the midtones that you ..like a red shirt , hair , the ocean etc ..that you can see the differences . Maybe its my lack of technique in post processing but I find it hard to match the .NEF files made with Nikon lenses to anything produced by a Leica DNG .
The Leica R glass on the D800E is the closest I can get . But I find it very difficult to match the Nikkors ,the Leica R and the Zeiss glass in a collection of images .