The best way to describe what I am seeing is to review the attached screen shots.
SelectedSlickEditCheckboxWithFocus.png shows what a selected checkbox looks like inside SlickEdit's preferences when the preferences window has the input focus.
SelectedSlickEditCheckboxWithoutFocus.png shows what a selected checkbox looks like inside SlickEdit's preferences when the preferences window does not have the input focus. It is rather difficult to see the check. To see this, open preferences, go to Fonts under Appearance and then, alt-tab to another running application. When I did this the first time, I thought SlickEdit had turned off selected radio buttons and check boxes.
For comparison purposes, SelectedSafariCheckboxWithoutFocus.png shows a selected checkbox inside Safari's preferences when that preferences window does not have the input focus. Notice that the check is clearly visible.
This is impacting checkboxes and radio buttons inside beta 6.