I listen to a lot of things Alf says, there are times when what he says is actually true. Alf mentions Sligs having beady black eyes, but that wasn't even the focus of the question, I think he released that info by accident.
Though there is a MO pic of a Slig that you can see passed his visor and he has beady black eyes.
I'm your man when it comes to Sligs, I mad search for any official say on anything about them.