In case you have not seen this but it looks like Sigma is working on fixing the color issues with blue skies being cyan and issue with reds. Seem they have corrected it, new firmware for all Quattros and a new version of SPP.
Here is an example:
The difference of color reproduction between the latest firmware and the conventional firmware?SIGMA CORPORATION
Alan
Here is an example:
The difference of color reproduction between the latest firmware and the conventional firmware?SIGMA CORPORATION
Alan