Hi Wotto
I installed the multi-coloured skull pile LEDs on my SS quite some time ago.
Nino is correct, during game play each of the skull's 6  pairs of eyes light up and the colour corresponds with the currently lit insert(s) on the "Six Tales Of Terror" p/f panel.
I bought mine as a complete set from Freeplay Amusements along with the very cool Dancing Boogiemen kit which works perfectly too.
I can't think why your skull pile LEDs are not performing properly.