Sigma has been updating their software and firmware more often than this site has been updated. Therefore I thought it might be a good idea to list where we stand today.
Sigma Photo Pro is now at 6.3.2 for both Windows and OSX. Besides many bug fixes there have been substantial improvements in the processing engine. Especially the last update supports the vastly improved color reproduction of the dp Quattro series cameras with the latest firmware.
Download Sigma Photo Pro here: http://www.sigma-global.com/en/download/cameras/sigma-photo-pro/
With the latest firmware update for the dp Quattro series cameras Sigma changed the color reproduction considerably. Skin tones are more pleasing, skies are more blue and contrasty and reds do not get saturated as fast as before. To see the differences in processing you can have a look at the following page: http://www.sigma-global.com/en/download/cameras/firmware/color_reproducibility/
The firmware is available for download at the following sites.
SIGMA dp0 Quattro cameras: http://www.sigma-global.com/en/download/cameras/firmware/#/dp0
SIGMA dp1 Quattro cameras. http://www.sigma-global.com/en/download/cameras/firmware/#/dp1
SIGMA dp2 Quattro cameras: http://www.sigma-global.com/en/download/cameras/firmware/#/dp2
SIGMA dp3 Quattro cameras: http://www.sigma-global.com/en/download/cameras/firmware/#/dp3
Notice: RAW data (X3F files) taken with the dp Quattro series cameras after the firmware update has been installed cannot be processed in software prior to SIGMA Photo Pro 6.3.2. Please use the latest SIGMA Photo Pro 6.3.2 to process for the latest RAW data.