We need to set a "Shading" (function as shown in an attached capture from Word) for a given document’s Run. Unfortunately, it seems this property isn’t provided in CharacterFormat. We tried to use HighlightColor property but this one has only a limited set of colors (see the other attachment) so this isn't an option for us.
Mario at GemBox
This feature request has been implemented and is available in the latest versions of GemBox.Document.