That's all digital work (Wacom Drawn, Digitally Airbrushed, etc)
Try using the Airbrush, and set modes for it (Hard Light, Overlay, Color Burn, Etc) and with your specific color, start brushing and messing around that way.
Another way to do is if you have an outline of your drawing, you can start by making fills of solid colors, and then shape the shadows and blends with the Color Dodge/Burn tool, along with the Airbrush.
Hope that helps,