Hi, Kit. I've also decided to give the Nex-7 a shot. My ZM 35/2.8, 35/2 and even the 50/1.5 all show varying levels of color shift on the camera.
My Nokton 35/1.4 does not show shift, but, like on the 5N, it has so much field curvature that the corners are never even that sharp at infinity at f8, unless you focus the center past infinity.
I'm currently using the Contax G 35. There is no color shift to speak of, and while not as technically sharp across the frame as my ZM 35s, it's a nice rendering lens. The G 35 is essentially identical to the 35 Summicron IV, but with Zeiss coatings. If you can stand a little longer focal length, the G 45 is the Nex-7 is about the sharpest digital camera-lens combo that I've ever used. Amazing lens. Eventually, I plan on getting these lenses converted to M mount, so that I don't have to deal with the fussy focusing rings on he adapters.
The CV 35/2.5 has had issues in the past on Nex, so I'm not real confident of how it would perform on the 7. It looks to me that the Sigma 30 is likely one of the best options around for a Nex standard. I'll probably get one, too.