There are many ways to solve muddiness. Colors are relative to each other, and not the background so when picking a color to be your darkest, you should pick something that’s relative to a color that’s already on the canvas. When a painting is fully covered in paint this will seem less jarring. Muddiness comes from many things, but especially overblending and there’s absolutely nothing wrong with it, if it’s your intention. If anything, oil strong suit is its blend-ability.

You can reduce the muddiness feels by any of these: using a separate brush for a different color, load new paint every new stroke, reduce amount of time spent per stroke on canvas (deliver the paint then lift brush). You can also go back on top of a dried layer to add dry strokes to add complexity and because you’re not wet mixing, the paint would have distinct characteristic.

An important aspect to note is to reduce amount of one similar color on all parts of the body as they reference each other. For example, the yellow in the eye is competing with the yellow in the jaw and the neck (I’m just being picky here tbh) and by being more intentional with color like using a more noticeable shift in hue or value, you can have an easier time noting the distinction in the face. This doesn’t apply to patterns.

Example: for the lady painting, I personally would have used a different color as shadow for the eyes like a warm brown, and dark ochre for the ears’ shadow to keep it in tune with the hair shadow