A common colour in Europe is a neutral pastel brown or beige tone that is neither too warm nor too cool.
The undertone of European skin can be neutral, pink or slightly yellowish. People with a pink undertone often have bright, rosy cheeks, while people with a yellowish undertone have a warmer colour. These undertones give the skin a certain vibrancy and individuality. 
Pastel brown tones, which are generally lighter and more muted, can be achieved by mixing in white. This gives the skin a soft and natural look. When painting a portrait, it therefore makes sense to use a combination of opaque and transparent colours. This allows the different nuances of the skin to be realistically depicted and gives the portrait a lively and natural look.

Brown tones are mixed in unequal parts from the complementary colours, e.g. orange and blue. To reduce the intensity of an orange tone and shift it towards brown, add a little blue. This breaks up the colour tone and creates a natural brown tone. If you increase the red or yellow content of the orange, you will obtain a more reddish or yellowish brown tone. Alternatively, existing brown tones from the Schmincke range can of course also be adapted accordingly.

I skip the basic mixing of brown tones and use the colours burnt Sienna (28604) and brown Brazil (28602) as a base for mixing the skin tones.
As burnt Sienna is a reddish brown tone and brown Brazil is a yellowish brown tone, these two colours are perfect for the base of skin tones. By adding primary magenta (28304) and violet (28305), I achieve further nuances of warmer or colder colour tones. By adding neutral grey (28701), I achieve deeper shadow tones.

I usually create a base layer with opaque colours and then overpaint with transparent colours.
By using opaque colours (i.e. by adding SUPRA-white, opaque (28101)), I achieve the necessary pastel tones in the base layer. I can now continue to use transparent colours in thin layers to create the desired skin tone and work out structures. It is also possible to erase structures. When working on canvas, I have the advantage of being able to spray structures with my opaque colours.
I start by mixing an opaque, neutral brown/beige colour. For this purpose I use SUPRA-white, opaque - burnt Sienna and brown Brazil.

The premixed basic shade, opaque, forms the base and can now be mixed further to create the following opaque colours/shades.

By underpainting with opaque colours and reworking transparently, you'll have the advantage of erasing the skin structures. The opaque underpainting in the erased structures is preserving a natural and harmonious colour tone, as the white of the painting ground is not erased.
When working on canvas, where erasing is not possible, skin structures can simply be sprayed lighter with the mixed base colour, opaque or base colour before being reworked transparently.
If the painting becomes too dark, it can simply be lightened again with an opaque colour. Or if a mistake is made, it can be corrected and reworked with an opaque colour.

You have to get used to using opaque colours or white, as these run through the spray gun a little slower. In addition, the annoying cleaning of the spray gun when changing from opaque to transparent colours requires a little more attention.
As I work exclusively on canvas and constantly alternate between opaque and transparent colours, I got used to use two spray guns.

Highlights and shiny areas of the skin are essential. This is what adds vibrancy to a portrait. I make these highlights lighter in the painting with the base colour. If necessary, the colour tone is lightened a little further with SUPRA white, opaque.
Finally, you have the option of using the mixed base tone, opaque, which can be diluted with a little water for this purpose, to carefully and very thinly rework the portrait in some areas. This allows skin structures to be softened and light areas of the face to be emphasised. If necessary, this can also be used to shift the skin tone back to a more pastel shade.

TIP: All mixing ratios for this report have been counted exactly, but only serve as a suggestion. You are welcome to work "freely" and it is always worth experimenting with your own mixing ratios, especially as every skin type is unique.