1. Environment effects skin tone: look for reflected light and color!

2. Human skin is translucent
Human skin is translucent. Translucency is especially noticeable in infants and the elderly. Pay attention to light passing through the skin of ears and finger edges.

3. Always paint the shadows on the skin first, keep them separated from the lightened parts. Use different brushes for lightened and shadow parts and (important) never use the same color or tonality for the reflected lights as you used in the direct lights.

4. Volume is not only rendered by color but also by the brushwork
Volume is not only rendered by color but also by the brushwork. And this should match with the underlying bone and muscle structures.

5. Cadmium Red as a transition from highlight to shadow and on ears, noses and fingers.

6. Begin by selecting an area of the face that falls within the middle tonal range, illuminated and rich in color. Mix this color on the palette. This will be your base skin tone. Mix a substantial puddle, as most subsequent skin tones you mix will branch off of this puddle. The puddles off of puddles method refers to the practice of starting out with a base color, and adjusting its hue or tone by pulling off a piece of the main puddle and introducing other colors. It can be very helpful: It will keep you from having to constantly remix from scratch slight variations of a previously laid skin tone.
Cadmium Red Light

7. All these skin tones were created by using these three colors plus white.

10. Beware of poorly printed photo reference….
this is the same artwork taken from 2 different websites.