Yes, thanks, I got the ones you provided to work. A quick note for absolute rookies like me: make sure Colors is set to 1 or there will be problems.
1) Mode: Subtraction
Color: Off / Black
Index: 0
Colors:1
Start Intensity: 1
End Intensity: C
Duration: 0
Another question: I want to extend the fade in duration. Do I need to increase each Duration parameter by the same amount?