Dithering - Joe the Echidnafox

To begin this technique, it is best to remove all of the shading from the area of your chosen art piece. As above, we have removed Sonic's head colors and we've prepared our palette. For this technique you may use as many colors as you like, and in this example, we will be using the three default blue shades from Sonic's sprite.

Next, start with the lightest shade, and make a light area similar to the one from the light sourcing tutorial, except it needs to be made of pixels that only touch diagonally.

Now, for the second shade, fill in the rest of the areas with diagonally touching pixels that appear right next to the lightest shade's pixels.

Lastly, fill in the rest with the darkest shade. And with that, we should be done. Now, you can also do this with any body part you want, and not just the head. You can also use a combination of dithering and other shading methods to give the illusion that there are more shades of color than what's you are actually using.