Monochromatic
So just as in the red/green complimentary still life, the image above with this young man with a blue shirt can produce some strange effects. His skin is brown. Brown is a shade of orange. Orange and blue are compliments. That will then yield skin tones that can appear gray, dull, dead and perhaps what you would want to avoid in a painted portrait. You can correct this by ignoring the complimentary admixture or by giving the sitter a wardrobe change. Putting him in a yellow or red shirt would be an analogous combination like our earlier painting and yield harmonies rather than grayed down color results.
The gray square above is a sample of color from under his chin. Does that look like healthy flesh?!
Painting I 