I know I need to learn to "see". I have figured that out on my own. From copying pixel art pixel-by-pixel I feel I have improved. I guess I'll copy pixel art hair too. I need to get an answer from someone about this.
Ai- I don't understand how on that loomis on hair 59-60 is learning about the hair. It's Analysis of facial markings and drawing faces of all ages. Did you give me the right page?
It also covers hair. Look how he starts by marking out chunks of hair. dividing them into broad planes and shading those planes. Then he divides up those chunks and refines the shading. You can see he uses this for the face too (meaning that the exact same methods are applicable no matter what you are shading)
Oh! I may have had an epiphany. I feel that the hair strands that are sticking out to your camera (pixel art or not) are highlighted so that's why the second character from the right is highlighted there. The hair that is top right is also sticking out towards you so it's highlighted. If the hair is depressed, there is less light than usual. Please tell me if it's true.
Sort of.. Shading is all about "how much light can reach your eye". Light hits a surface and bounces off. If it hits your eye at all, then the surface doesn't appear totally black. The more rays hit your eye, the more the color of the surface is revealed. Specular Highlights occur when there are an overwhelming excess of rays hitting your eye.
The whole thing is about angles. Highlights mostly appear on parts of a surface that are facing fairly directly towards the viewer (this is the circumstance in which it's easy for the most light to get to your eye). On faces that are not pointing directly at the camera, highlights are possible but it requires proportionally more light to produce a highlight (since a percentage of these light rays will bounce off in a direction that *doesn't* hit the eye)
Naturally, less light rays manage to hit recessed areas to begin with.
So 'what is sticking out' is one part. 'Where is the light source' is another (for example, you wouldn't expect highlights on the front of the object if the lightsource was behind the object)
The third guy from the right doesn't seem any different in this regard -- I guess he is lit from the front+above, creating the ring of highlights you see.
But this is one of the reasons people recommend study from life. An artist's portrayal of light is always imperfect and inconsistent to some extent, nature is not.