Before & After:
Open image. Duplicate the image. Next, create a new blank layer. Let's name this layer “Girl-Skin”. Fill layer with color using the Paint Bucket Tool (G). Pick a color closest to skin tone using the Color Picker. Later, change the Blend Mode to Color.
Next, click on the Vector Mask icon situated at the bottom of the Layers palette. Click on Ctrl/Cmd+Backspace to invert the masking layer. You will see that image has returned to black and white on screen. Start masking the area of the model's skin using the Brush Tool (B) and the skin color will appear.
If your layer mask is black in color, then the color of your brush would have to be the opposite i.e. white in order for the effect to take place. If you've made a mistake, simply brush the area again but this time, switch your brush's color to black i.e. the same color as your layer mask.
You can use larger a brush size to recover the B&W background. When it comes to finer areas which require more careful detailing, smaller and softer brush size will be a more suitable option for masking.
Note: Remember to adjust the Opacity, and the Hardness level of the Brush for softer masking edge.
The parts that I've circled have finer details, so we must be more patient and perhaps spend some time to remove the unwanted skin color.
Once we're done coloring the model's skin, I then created a new layer to work on the hair and repeated the same steps. Do the same with the assessories. Pick a color of your choice for both hair and accessories. Plan and work on coloring the different parts one layer at a time.
For the remaining areas of the model, we can adjust the colors using the various options from the Adjustment Layers. It allows us to modify and change the colors if needed. Do this by clicking on the Adjustment Layer icon at the bottom of the Layers Palette. Always press Ctrl/Cmd+Backspace to invert the masking, so that it won't affect other parts of the image and only mask out the area that you want. We can thus proceed to color the model using the same method.
For the eyes, I click on the adjustment layer and chose to tweak my color settings using the Color Balance option. Invert the adjustment layer and then apply the brush to mask out the model's eyes. That's easy, right? :)
On the image layer, I selected the area around the mouth quickly using the Lasso Tool (L). Next, I created another adjustment layer and named it 'lips'. This time, I chose the Curves setting option and tweaked the settings until I get the red I wanted. Invert the adjustment layer. Then apply the brush to remove the access color.
Adjustment Layers will let us modify or adjust the color anytime so you can tweak the colors once you’ve completed painting. This is very useful because we don’t usually get the color right the first time and would need to make adjustments when we’re done.
Once done with masking, we can arrange and compile all the model's layers under Layer Groups. I named mine “Girl”. Layer Groups are great for managing and organizing your layers.
To create a Layer Group, select the layers you want to include. Then go to Layer > Group Layers, and the selected layers will be automatically placed in a newly created folder. For a new Layer Group folder with no selected layers, click the New Group Button (the folder icon) at the bottom of the Layers Palette.
Next attempt will be the two men and background. We will still use the same easy way to produce color for them. We'd only need to be extra careful when comes to details. Zoom-in as big as you can when coloring. Also, remember that you can always adjust and change the color using Adjustment Layers. After that, simply group the layers into your respective Layer Groups to avoid messy layers.
Once the basic coloring is done, we now enhance the mood of the photo. Use Adjustment Layers like Curves, Hue/Saturation and Color Balance to boost and enhance the color of the photo. Here's mine but you don't have to follow my settings... feel free to explore and tweak the settings until you are satisfied with the results that you want.
Lastly, Flatten the image and save file. :) Voila! My finished result.