The Project Settings > OCIO tab allows you specify an OCIO configuration file other than the one supplied with Nuke.
• viewer process LUTs - Specifies whether viewer processes use Nuke’s native LUTs or OpenColorIO LUTs.
• OCIO config - Specifies the OpenColorIO configuration file to use. The dropdown menu lists all of the OCIO configuration files stored in any of Nuke’s plug-in paths. Select custom from this menu to enable path to custom OCIO config below.
The OpenColorIO configuration file contains all of your colorspace definitions. The one you select determines the colorspaces that are available in the OCIO nodes.
• path to custom OCIO config - Select the custom OpenColorIO configuration file to use.
If you have specified an OCIO environment variable (for example, OCIO="/myOCIOConfigLocation/config.ocio"), Nuke always uses the configuration file specified there. In this case, the OCIO config and path to custom OpenColorIO config controls are disabled.