No... I used Paint Shop Pro and told it to Add Mask based on an inverted copy of the layer's Luminance and then hit the layer with a black Fill with the tolerance set at 100%. I always do this so I can paint the colors underneath the outlines, but it also lets me recolor the outlines if I ever want to.

But your solution is intriguing too. The only question is, how well does it hold up if there's another layer under the outlines?

Yeah, I use PSP too.

What I know is that screen works like the opposite of multiply: it multiplies the inverse of the current layer with the inverse of the underlying layers, then inverts them all back again. (In mathematical terms: if multiply does x = a * b, then screen does x = 1 - (1-a) * (1-b) )

If that makes no sense, just think of screen as a version of multiply that makes things brighter instead of darker. Screening with black gives the colour you paint with, screening with white gives white.

I tried it out just to see what the result was: