This color shift effect is not the same as vignetting. It is a real and annoying problem. I had it with my Kodak SLR/c. It is to do with the sensor design.
Experience seems to point to this being a bigger problem with the larger resolution chips. The problem is usually worse with wide angle lenses where the light rays are at a steeper angle of incidence to the sensor plane.
From various sources I have assembled the following summary.
Aptus 22 - No problems of this kind
Phase One P25 - Some problems of this kind compensated with Capture 1 and LCC shots
Phase One P45 - More extreme version of P25
Aptus 75 - Some problems reported with Wide angle lenses (eg: Schneider 35XL) but only at shifts of 20mm +
People differ about whether this is a problem for them or not. For me it is a potential problem.
I would like to go down the Aptus 75 route. My worry is that there may be subtle issues with wides with non extreme shift angles. These issues might only emerge when photographing, say, a minimalist white interior... but then it would necessitate more work in post.
I notice that the Rodenstock Sironar Digital 35 has a wider image circle, and longer flange focal length than the Schneider 35XL. Perhaps it will suffer less than the Schneider 35XL when used with the Aptus 75 as the angle of incidence of the light rays will be lesser than with the Schneider. However... all this is making me quite concerned as it is virtually impossible to test all the options prior to purchase. I have no information about the distortion or other characteristics of the Rodenstock lens and dealers do not typically stock them. In addition, the exotic platform I would need to mount the 35 on means that the lens I would like to test needs a weird and wonderful mount!
My gut feel is that we are still at the bleeding edge, where purchasing decisions might need to be reversed at significant cost if errors are made.
The lack of standardisation in the camera platform area is a real minefield. For example. I can buy a sliding adapter for my Cambo Ultima. But it only allows switching between portrait and landscape format if I buy an H1 fitting digital back...
However, I already posess a full suite of Mamiya lenses, and do not want to have to replace the Mamiya with Hassleblad gear.
So far I can't find a way of using MFDB for my work without buying at least one (and possible two) new camera platforms. (I already possess two view camera, one MF and Canon SLR platforms, so I am running out of glass cabinet space!)
Add this to issues like this color cast... and I am finding the process of getting into MF digital extremely complicated and error prone.