Open the picture and for my pic the resolution not so good..so I want to adjust the resolution. Firstly duplicate the layer Ctrl+J. After that for the new layer you change the mode Normal to Overlay.
Go to Filter> Other> High Pass
I setup 23.3 pixel and the you must change the mode from Overlay to Hard Light
You see the pic more better right..Hehehe...Ok lets start to add color in this picture. Actually to add the color is easy. Depends in your creativity. You must Merge Down the first layer. So easy to you for the next step. Right click> Merge Down.
You must Duplicate the layer. And then go adjustment layer> Solid Color
You choose the best color for skin. Click OK
Click Layer Mask Thumbnail> and then go to eraser. Now select the eraser tool and erase all the areas that brown/yellow isn't part of the skin. If you make a mistake, simply select the brush tool and paint back the area that you accidentally erased. Use a brush with a hardness of about 50 or higher or else you'll get a halo effect in the final outcome.
Repeat the step 8
After finish to colorize. Right click every layer to Merge Down and go to Image> Adjustment> Brightness/Contrast then go to Image> Adjustment> Vibrance...Setup it with our own creativity..
That all...Good Luck