I specifically choose the Curses trait “Chilling Darkness” because I thought that it would synergize well with Reaper greatsword skill #4 (Nightfall). However, unlike the “Well of Darkness” utility which shows the Chill, the tooltip for Nightfall does not show the Chill effect.
Testing the skill out in-game, it looks like the Chill is applied in addition to the Blindness, so I think it’s just the tooltip that doesn’t work.