Layer Settings, Gradient Maps and some colouring. (PS7)
This is a basic colouring effect tutorial. It's not an earth shattering technique, and has undoubtedly been done before, but it's effective and people should really learn to work with the original picture before covering it up with brushes.
So we're starting with this;
and we're going to end up with this:

Cap a la New Atlantis - The Evolution who do a great line in high res Stargate Atlantis caps. /pimp
Obviously I've selected the part of the pic I want and cropped and resized it at this point.
Next thing I do is duplicate the layer (always do this if only for your own reference) and then sharpen the new layer. If you don't know how to do this already you're really aiming over your head and should go and play with your program some more before attempting anything else. Boring I know but if you want to make pretty them's the facts.

Better. But I know a little trick which will make it better still. So duplicate the new layer and go to 'Filter' > 'Blur' > 'Gaussian Blur'. Set the radius to 5.0 pixels and hit 'OK'.

Now you're thinking I'm crazy. You'd be right but I prefer the description 'evil genius'. Means the same thing but has a better ring to it.
It's what we do with this new blurry layer that makes all the difference.
Go to your layers pallete. See the little drop down box that right now says 'Normal'? Should look something like this;

There's a drop down menu that you open by clicking on the wee arrow. Select the option 'Overlay' on that menu.
And it will do this to your blurry layer;
Now the colours are magically richer and deeper, Elizabeth's skin is smoother and the picture has a pretty glow to it.
And you've just learnt how to change a layer's setting. Bonus.
Now for the ubiquitous blue exclusion layer.
I used the shade #1A1F50 in a new colour fill layer set to 'Exclusion' at 100%.

Bit too blue for my liking so I added another new colour fill layer this time of #9F9958 which is a kind of caramel brown colour. This layer I set to 'Soft Light' again at 100%.

It's almost there but along the way we've lost some of the depth of that wonderful colour so to get it back I add a gradient map.
Sounds scary? It's really not. Back to your layers pallete.

See that wee black and white circle I drew a big red circle around? Click it and you get a menu. Click on the option on the menu that says 'Gradient Map'.
Now this is the box where you make the gradient map. The colours you see right now are the colours I had selected at the time. So to change the gradient I clicked on the wee arrow to get the drop down menu.

Ooo look it's the default gradients. Select black and white (third from left). Hit 'OK'.

This has created a new layer that has turned Elizabeth black and white. Oh no! She's trapped in an old movie! :-o

So go back to your layers pallete and change the setting of the gradient map layer to 'Soft Light'.
Et voila.

We've got the depth of the colouring back and finished the colouring effect.
Hope this is helpful to someone.
Note: This icon is up for grabs. Credit to jacksrubberduck or
kharismaticicon please.