1. Photo Manipulated
Original

2. Step One
Upload your original photo and set it right side up by using the rotate option under the image tab.

3. Step Two
Go to image > Adjustments > Auto levels, and click. This will balance the light on your image.
This step is not necessary for everyone but in most cases it helps, if it doesn’t just use the undo feature.

4. Step three
Before starting any coloring copy the background layer by right-clicking it and selecting duplicate layer.

5. Step four Be sure that layer is set to Multiply
Also name the layer according to what you are coloring, for instance skin
Next Make a new layer.

6. Step five
Now select the magic wand tool and in the background layer click on everything but the skin, then click back on the skin layer and hit the delete key. This should remove most extra color from where it shouldn’t be. Anything it misses you can go back at with the eraser tool.
Select the skin layer and using a skin tone or skin like tone from the color pallet then using a brush color in all skin areas
It doesn’t matter if you mess up the next step will explain

7. This technique should work for almost anything
This technique should work for almost anything. However there are times when the magic wand selects more then you would like. When this happens you have two options.
First you can go back and manually erase the color on that layer (adjust flow and opacity of the eraser for a smoother color transition)
Second would be to extract the figure or object into its own layer.

8. Extracting
If you go to filter > extract this window will pop up.

9. Once the figure is fully outlined use the paint bucket tool to fill it in.
Then using the zoom function highlight the outline of the figure you wish to keep carefully.

10. Now that your figure is one color hit ok and now everything around that figure has been erased.
It’s not perfect but it helps a lot on occasion. If you are having difficulty with any part of coloring the best thing to do is explore, if anything goes wrong just use the step back function.

11. Using these techniques may or may not work for you, this is just what worked for me. There are also many tutorials on the web that you can consult should you have difficulty.
That website has many useful tutorials and most drawn figure coloring tutorials will work with a scanned black and white photo as well.