Try an "ON" effect. For the color, right click on the color to select the color curve. Put two of the little sliders on the color curve, and drag them to the two different sides (left and right). Make one of them Black, and the other white. Set the blend mode to Random. The colors then look like a bar code, with lots and on and off. They change so quickly that they will look like a flickering flame. I used that in pumpkins for halloween and people though it was a real candle in there.