Disclaimer: This info is all coming from my brain. Some things regarding shading may be unique to me and therefore unconventional or incorrect.
Shading with a grayscale layer allows me to shade skin and anything else without muddiness. I think it’s important that a couple things are kept in mind:
Have a lowest, mid and highest value ready to go. Use a grayscale pallete if you want to (you can easily pull one from Google)
My highest value is almost white. My personal lowest value is usually #808080 which is directly in the middle of black and white. I never go darker until after the entire subject is shaded.
«Quick, real time demonstration. I started off blocking in my values using the three grays to the left: #808080, #bfbfbf and #f2f2f2. Any values in between those where color picked from the resulting overlaps. Eventually, I had a nice gradation and gently blended everything into a smoother gradation (for this smooth, round surface) using the smudge tool. A large, soft-edge brush was used to add a general highlight and ambient lighting in the end.
- Try shading from your lowest value to your highest (making use of a tablet’s sensitivity).
For some, understanding values may be less obvious than for others. I personally use a lot of on-the-spot intuition (because after you’ve done something enough times, it becomes a repeated process applied over and over again). When you have a light source hitting an object, you need to know which part(s) of that object get hit with no light, a little bit of light or a lot of light. Shading from your lowest value to your highest value may assist your eyes when determining this:
«Quick, real time demonstration. This is essentially how I do Annie Mei’s green orbs!
When you’re all done with your shade layer, set it to Multiply on top of your flats layer and see what you got!
I’m not very good at explaining things but I hope this helps out in some way when it comes to understanding shading in general.