This morning, Sigma support suggested that I use a preset white balance rather than Auto as I have been using.
Since the time I started with the Olympus E-1 and now with the Nikon D300 I’ve always used Auto WB and corrected/manipulated later. This approach won’t work with the current algorithms in SPP for me and the presets seem to minimize the problem. The Oly had an external sensor that seemed to nail WB and NIkon does better than I could ever guess at.
It seems to be a complex interaction between colors in the image and brightness that leads to the software rendering the dimmer edges with a green bias. I’m more confident that Sigma will be able to improve this in SPP. Even if they never got it any better, this image once again shows the potential of this compact.