Using the PxrCryptomatte workflow, you can output IDs in Solaris for easy selection in a compositing application, which you can then use that selection as a mask to make changes selectively in post-production.

PxrCryptomatte is supplied as a Sample Filter plugin. As such the output for Cryptomatte is stored as a separate EXR file from your beauty or denoise outputs. Please note an OpenEXR is required to store the values correctly.

The above example will output a separate Cryptomatte exr file and assign a unique matId for each material in the Solaris scene.

Once rendered, you can then use software like The Foundry's Nuke to isolate a particular material or object in the scene.  In this example, we have selected the back wall in the studio, using the Cryptomatte Nuke Gizmo




and from there we can use that output as a mask to drive a ColorCorrect node to gamma down that particular part of the image to enable the foreground elements to stand out further from the background.

For more detailed information about the Cryptomatte Sample filter, this can be found on the dedicated PxrCryptomatte page