Hi EleanorB, Thanks for contacting us! You can change hair color on the Touch-Up tab using the Highlights effect. Select the color and then paint on the effect by dragging over the hair on your image. Let us know if you have any further questions!
Thanks for reaching out to us! I’ve shared this feedback with our product team so that we can improve the Highlights tool to support further darkening. In the meantime, you can apply the effect and then apply it again over the top in order to darken the hair further.
Let us know if you have any further questions or feedback.