I'm starting with this: (cap from http://www.vm-caps.com)
Duplicate it and set the top layer to Screen. Sharpen the Screen layer (Filters > Sharpen > Sharpen). And I have this:
Because this is still dark, I add a Curves layer (Layers > New Adjustment Layer > Curves). On the RGB channel, click somewhere in the center of the line, and move it up, to lighten up the icon. On this particular icon I used this. Now Merge Visible (Layer > Merge Visible). And I have this:
Open a new Curves layer, and Adjust the RGB to lighten the icon some more, and I usually adjust the Red, Green and Blue channels as well. For this icon I used: RGB, Red, Green, Blue. I now have this:
Above the Curves layer, open a new layer for Hue/Saturation (Layers > New Adjustment Layer > Hue/Saturation). Leave Hue and Lightness alone, we're only going to use Satuation. I adjust the Master level as much or as little as I feel looks good. Usually I adjust the Green, Cyan, and Blue layers as well. For this icon I used Master: Saturation +5, Green: Saturation +45, Cyan: Saturation +45, Blue: Saturation +45. It doesn't make much of a difference yet, but now I have this:
Above the Curves layer, but below the Hue/Saturation layer, make a new Color Balance layer (Layers > New Adjustment Layer > Color Balance). Midtones: Cyan-Red -41, Magenta-Green -5, Yellow-Blue +31. Highlights: Cyan-Red -10, Magenta-Green 0, Yellow-Blue 0, and leave Shadows alone. This blue tint is from a tutorial by kryicons. I now have this:
On top of the Hue/Saturation layer, open a Selective Color layer (Layers > New Adjustment Layer > Selective Color). Red: Cyan -100%, Yellow +100%; Yellow: Cyan +100%, Yellow -55%; Neutrals: Cyan +100%, Yellow -40%. I set the Opacity to 53%. I have this:
On top, open a new layer. I decided to fill it with a yellow-beige, I chose #E9E6C5.
Set the yellow-beige layer to Soft Light, and set Opacity to 20%. I have this:
Above that, open a new layer. I filled it with a light blue, I chose #C6DFE9.
Set the blue layer to Color Burn, and set Opacity to 76%. Now I have this:
I'm finished with the coloring. See the Layers.
I hope that was helpful and clear enough to understand. :)