So you want to paint skin, but you're wanting to keep it simple. This might be because you are a beginner, just sketching, or just wanting to get basic colors because you aren't getting majorly into portraiture.
I've found that by using Venetian Red, Van Dyke Brown, and Ultramarine you can get a wide range of skin tone and their values.
I'm really into this triad because of the various textures. We have the granulation going on in the Ultramarine but then we also have opacity in Venetian Red. So we have simplicity in the mixing of flesh tone, but it ends up looking really interesting texturally.
I also like this because most people probably have Ultramarine and Van Dyke Brown (or a similar earth brown) but then you throw in the Venetian Red, which is a pigment that I hadn't worked with before and doesn't seem to be overly common in an artist's standard palette.
Above images are from the QoR website and aren't they amazing! Thats some next level swatching!
So when you are simplifying skin tone down this much you aren't getting results that are particularly nuanced, but its really great for sketching, practice, value studies, and planning for larger and involved paintings.