Fixture setting > Color tab
Select fixture #1 -> #16
Change RGB color to, lets say 25|25|25 to make them dark, and press Enter on the last one to make sure the number sticks.
Then click on either a random fixture and back to lets say #7, and "Fixture setting" say 125|125|125 but 3D view displays "black-ish".
If i close the 3DView window and re-open it, all but #16 are 125|125|125, where #16 keeps it at 25|25|25.