Hi Brenda,
Use this one: ToggleSelectionHighlight.rvb (1.6 KB)
Save it on your computer and drag-and-drop into Rhino. From there, it will add an alias: ‘ToggleSelectionHighlight’ to run as a command. You can also make a button that calls ToggleSelectionHighlight command. I will let you figure out how to do that.
To bind it to a key combo, go to Options > Keyboard, find a combination that works for you and add the same ToggleSelectionHighlight alias.
–jarek