Lightning - Modifying Opacity

Basically have made a spell involving lightning & trying to improve the visuals of the actual lightning streams themselves.

How do you make it say 50% opacity. I tried both of these but it led to the lightning simply becoming invisible:


I thought the last one was the opacity, just like with a unit?

And it is, though I believe that the alpha integer only goes up to 100 :S

So, 50% should be this:
call SetLightningColor( lightning, 255, 255, 255, 50 )

Valid range for the parameters r,g,b,a is [0.0,1.0].

thx for help guys ( 1, 1, 1, 0.5 ) works perfectly.