I’m not sure exactly what style you’re rooting for so I went more semi-realistic for the example paint-over, but I think if you struggle with hair then look on studying form structure. In the paint-over I added more form to both the hair and the face to give you an example of how form could help you with portraits. To study form, go over values (greyscale studies), planes (Asaro head and simple shapes, lighting) and face structure. The colors you picked here are great and you know the facial features well, it’s just about adding more form here and it’ll upgrade your skill a ton

