I've never seen a tut for this. Ever. AND it's super easy. I'm going to teach you how to take an image, and put it on it's own layer, while keeping all the shading.
And go from:
to 
But don't let my lame color choice discourage you.
So first off, you take your image, and make a new layer above it, and fill it with whatever you want. Solid colors, textures, brushes, even another picture. I just used plain purple for the sake of the tutorial, then used Ctrl->A to select all and Ctrl-C to copy it.
Next thing is to click this weird little button over here.
Which when you paste (Ctrl->V) your image, it'll look like this. Weird, but not how it'll end up. This just shows you where the image will be.
When you click the button NEXT to the one you pressed before, it'll look like this. All the shading has been selected.
Press delete and it'll look like this.
You could leave it like this if you want, but it's really ugly.
Now either hide or delete the background layer, and fill a new layer UNDER the line layer with whatever you want. I used light blue.
Now it's really starting to look like something. See, all the shading is still there, but you're now free to do anything with the layers. I decided I wanted the background more blue, and changed it.
Then I decided I wanted the foreground more pink...
Lastly, to make it just a little more interesting, I used some brushes on the pink layer to make it look cooler.
Lastly, crop your image if you want.
This works really great with balck and white manga images if you want to put a gradient or texture on top of it, or color it.
Done with Photoshop 6, but possible in Paint Shop Pro.
And go from:
But don't let my lame color choice discourage you.
So first off, you take your image, and make a new layer above it, and fill it with whatever you want. Solid colors, textures, brushes, even another picture. I just used plain purple for the sake of the tutorial, then used Ctrl->A to select all and Ctrl-C to copy it.
Next thing is to click this weird little button over here.
Which when you paste (Ctrl->V) your image, it'll look like this. Weird, but not how it'll end up. This just shows you where the image will be.
When you click the button NEXT to the one you pressed before, it'll look like this. All the shading has been selected.
Press delete and it'll look like this.
You could leave it like this if you want, but it's really ugly.
Now either hide or delete the background layer, and fill a new layer UNDER the line layer with whatever you want. I used light blue.
Now it's really starting to look like something. See, all the shading is still there, but you're now free to do anything with the layers. I decided I wanted the background more blue, and changed it.
Then I decided I wanted the foreground more pink...
Lastly, to make it just a little more interesting, I used some brushes on the pink layer to make it look cooler.
Lastly, crop your image if you want.
This works really great with balck and white manga images if you want to put a gradient or texture on top of it, or color it.
Done with Photoshop 6, but possible in Paint Shop Pro.