Involves Selective Coloring and Exclusion, non-translatable. PSD upon request. Using PS CS4 (but capable for people with 7.0 and above).
1. Take your base and crop it to a 100x100 icon.
2. Duplicate the base, set it on Screen at 70% Opacity, 70% Fill.
3. Duplicate the Screen layer, set it on Soft Light. Then, go into Filter>Blur>Gaussian Blur, and set the pixels at 2.0, and hit OK.
4. Add a Hue/Saturation layer (Layer>New Adjustment Layer>Hue/Saturation), set it at +31 saturation.
5. Add a black and white Gradient Map (Layer>New Adjustment Layer>Gradient Map). Set it on Multiply, and bring the opacity down to 40% and the fill to 70%.
6. Add another gradient map, this time, I used the colors #00031a and #360202. Set the layer to Screen.
7. Add a Selective Color layer (Layer>New Adjustment Layer>Selective Color). Put in these values:
Reds: -21, 0, +10, -8
Yellows: -10, 0, -21, 0
Blues: -100, +100, -100, 0
Blacks: -19, 0, -15, +21
8. Add another Hue/Saturation layer, with the saturation at +9.
9. Add a new layer and fill it with #360202. Set the layer on Exclusion.
You're finished! =3
Just as a small note, this tends to work best on dark icons, mostly black and gray, with bright highlights, with a tweaking here and there. Don't be discouraged if the first try doesn't come out successful, practice makes perfect, as they say.
Feel free to leave comments or questions here. =D I'll be more than happy to answer.