The short answer
No. Non-Muslim women do not need to cover their hair anywhere in Marrakech's streets, medina or souks. A head covering is only asked for inside certain religious sites, and most working mosques are closed to non-Muslims anyway. Many Moroccan women do not cover their hair either, especially in Gueliz and Hivernage.
In more detail
What matters more than hair is shoulders and knees. Covering those in the medina is the social norm for everyone, and it is what locals actually notice.
Carry a light scarf all the same. It weighs nothing, and you will use it: over your shoulders near a mosque, as shade on a hot afternoon, against dust on a desert road, or round your neck on a cold winter evening.
If you choose to wear a headscarf for sun or modesty, nobody will think it strange. It is simply not expected of you.
Inside the religious buildings you can enter, such as the Ben Youssef Madrasa or the Saadian Tombs, no head covering is required either. Covered arms and legs suit those settings better than a headscarf does.
Good to know
- Cotton or silk scarves breathe better in the heat.
- Keep one in your day bag rather than at the riad.
- Shoulders covered matters more than hair covered.