Made in Photoshop CS2, uses two selective coloring layers, but they're not exactly crucial for the coloring. I'm writing this assuming you know the basics of cropping, sharpening, blending modes, etc.
This tutorial sort of combines elements of this tutorial and my own favorite techniques. ^^ I came up with it while working on my most recent batch and was like OMG *USES IT ALL OVER THE PLACE* so I thought I'd share.
1. So here's our base, cropped and sharpened and all that jazz. Hi, base!
2. Duplicate the base and set the blending mode to screen. Duplicate this layer and set the blending mode to soft light. Fiddle around with the opacities of the two layers until you've got something that's bright and contrasty, but not blinding. ^^
3. We need some more color! Add a hue/saturation adjustment layer and up the saturation to +25.
4. Create a new raster layer and flood fill with #02010e. Set the blending mode to - you guessed it - exclusion!
5. I didn't like how orangey it was becoming, so I added a selective color adjustment layer and used it to add some blues back in, like so:
6. Now, add a new raster layer and flood fill with #e2e2e2. Set your blending mode to color burn and the opacity to about 80%. Oh we loves these layers, don't we~ XD Now we've got darker shadows and midtones, hooray!
7. Get yourself a new layer and flood fill with #110f38, set blending mode to exclusion, and lower the opacity to 55% or so. I also love these layers~ XD
8. 'Nother new layer, flood fill with #f49ac1 and set the blending mode to soft light. Leave the opacity at 100%. Don't worry about the overwhelming pinkness for now, we'll fix that in the next step. XD
9. New layer, flood fill with #a5f8f1 and set the blending mode to color burn. Now we have some nice blue tones in the shadows, but we get to keep the lovely pink tones in Aerith's skin.
10. Last new raster layer! This time, flood fill with #684718. Lower the opacity to 10-15%; whatever looks good on your icon. I used 14% for this particular icon.
11. You could stop now, but I decided I wanted a bit more reddish/pinkish tones, so I made a new selective color adjustment layer and put in the following settings:
This brings out the reds already present in the icon, and lightens up the blues in the midtones/neutral shades. ^^
And that's it! This is a fun coloring because it brings together all kinds of different layers. XD I really like the washed-out, sepia-esque effect you get with the brown layer on top. >3
Other icons made with this technique: