I wonder why transparency doesn't work with gradient maps to get very complicated effects. See thread here: http://forums.adobe.com/message/45434...
There are no easy ways to get something like this, using transparency gives always solid colors:
Right now, opacity settings in gradient maps appear to have no effect whatsoever. This is misleading - because, hey, why can we set opacity in a gradient if it doesn't do anything? But more importantly, if it worked, it would rock. By 'work', I mean if the opacity of the gradient was interpreted as a sort of smart layer mask for the application of the gradient itself.
As a basic test, create the following layers, top to bottom:
1. Gradient Map
2. White with black squiggles
Set the gradient map so that it runs from 100% opaque red to 0% opaque red.
What I see: the entire picture goes red
What I want to see: the squiggles go red, the white shows through.