Page 13-5 of the ClarisImpact User's Guide states that it is possible to change the "border, color, and fill, and add a drop shadow using the tools on the style bar" while a Note is selected.
However, changing these attributes for a Note is not possible. When attempting to change one of these attributes in the manner described ClarisImpact will simply beep at you.
You can change the size and text color of a note.
The Publications Department is aware of the the issue.