What application(s) do you use to convert the X3F file to your preferred output file? i.e. JPEG, TIFF, PNG, etc, etc?
Do you have a Gretag-Macbeth ColorChecker card?
The
long way round is to use Adobe's stuff in the following order:
RAW to DNG converter: makes a DNG file from your SD9's X3F file
DNG Profile Editor: lets you push the (color-picked) skin tone in any direction you like while affecting other colors as little as possible. The DNG image is not changed although it's preview on-screen is. Then you can save your efforts as a DNG camera profile (.dcp).
Adobe Camera RAW (ACR): open your DNG file and (ACR 4.4 onwards) select your new camera profile. Then your color adjustment is automatically applied to your output image from ACR.
The
short way is to mess with the color adjustment circle in Sigma Photo Pro - but other colors in your pic will likely be affected too.
good luck,
Ted