Simple coloring tutorial using Photoshop CS. Probably can be translated to other programs. Beginner tutorial but need basic knowledge of photoshop.
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Step 1: Prepare your base
I resized the image and cropped it to my liking.

Duplicate your base and set it to screen 100% Then Sharpen it once. You may want to sharpen it again, this really depends on your base. I only used one screen layer but you can use more than one or use a soft light layer. Once again it depends on the quality of your base. Blur the background or skin if needed, I only blurred the background.

Step 2: Layer>>New Layer(ctrl+shift+N)Flood fill it with #a6c6f6. Set to color burn 75%

Step 3: Layer>>New Layer Flood fill with #f6b086 Set to color burn 49%

Step 4: Layer>>New Adjustment Layer>>Curves. I suggest playing around with curves. For RGB channel i set it to 118-input, and 132-output to brighten it a little. If you would like a little more contrast and color in it play around with the color channels. Its always going to be different depending on the picture you used.
Step 5: I noticed some dark areas on the face I didn't like so I used the dodge tool with a soft round brush at 50% and on the screen layer I went over some of the dark shadows on the face.

Some other icons using this technique:

Go from
to 
Step 1: Prepare your base
I resized the image and cropped it to my liking.

Duplicate your base and set it to screen 100% Then Sharpen it once. You may want to sharpen it again, this really depends on your base. I only used one screen layer but you can use more than one or use a soft light layer. Once again it depends on the quality of your base. Blur the background or skin if needed, I only blurred the background.

Step 2: Layer>>New Layer(ctrl+shift+N)Flood fill it with #a6c6f6. Set to color burn 75%

Step 3: Layer>>New Layer Flood fill with #f6b086 Set to color burn 49%

Step 4: Layer>>New Adjustment Layer>>Curves. I suggest playing around with curves. For RGB channel i set it to 118-input, and 132-output to brighten it a little. If you would like a little more contrast and color in it play around with the color channels. Its always going to be different depending on the picture you used.
Step 5: I noticed some dark areas on the face I didn't like so I used the dodge tool with a soft round brush at 50% and on the screen layer I went over some of the dark shadows on the face.

Some other icons using this technique:

