tools -> options -> appearance -> Colors allows you to change the highlight in the edit window of the file you are editing. I need to change the highlighting in a Visual SlickEdit dialog box edit control. I suspect I need to play with the XWindow themes and resource settings. I'm not sure why this changed between the two versions of SlickEdit.
Update: I played around with the XWindow themes and colors. Other applications, like Gimp, responded to the change in edit control highlight colors, but Visual SlickEdit did not. Apparently, this part of of SlickEdit is not configurable. (Ubuntu 16.04.4 LTS, MATE)