Changing hair Colour from black to white.

I'm trying to get change the colour of hair in PS7 from black to white for a friend's icons. Previously I would use Layer via copy then change to colour overlay. I tried that but the white doesn't come out.

Is there a way around it?

Thanks

ETA

I tried changing some of it and came up with these



I made it with Colour blend set at Color and the layer set at Screen. It's not exactly smooth and I had to layer it about 6 times before I got the colour I want. Anyone got any idea?