For the shading on this particular skin I imagined a light source being on the top left of Saitama's head

then I shaded only the right side of the face with the darker tone first then found a good intermediate tone for inbetween the dark and the light

the suit itself is pretty standard but I realized if you keep the body a darker color and focus on highlights the highlights can create a sort of "implied line" for muscle which is what I like to use on most of my skins that have relatively buff physical features

I chose black as a good undershade as Saitama himself is a Anime character and black is a very good contrast to the normal skin tones of such characters and it fits as my imaginary light source on the top left would beam down and create such shadows


Ultimately its experimentation, for most of my skins I alternate between the 1st layer and the 2nd layer and see what is possible such as making unique shapes or shading in certain areas (Such as the eyebrows for this skin it combines the 1st layer and the 2nd layer)

I did not carry this light source to the rest of the body as I felt it would ruin its overall quality but the head design looked very well done so I kept the shading on the skin only

Thank you, also it is pretty cool