ensure your colour scheme is harmonious
Usually the biggest mistake in a portrait painting is the skin’s colour: it’s never either beige or black. Skin comprises a multitude of colours, from pale blue around the eye, pink, to hints of yellow for the mouth’s corners. I start painting with very few colours, and progressively add more hues. I save my colour palette in a corner of the illustration so that they’re always on hand. To avoid a muddy look, I avoid using pure black or white. Instead, I increase the saturation to the colour I using for the shadows.