You can wear black; this is generally considered appropriate to dress modestly and respectfully during Holy Week, which is the week leading up to Easter in the Christian faith.
Black is a neutral color that can be appropriate to wear as long as it is not worn inappropriately or disrespectfully.
However, the specific guidelines for what is considered appropriate to wear during Holy Week may vary depending on the individual’s cultural or religious traditions and the specific context in which they are participating in Holy Week observances.
It is always a good idea to consider the cultural and religious norms of the community in which you are participating and to dress in a way that shows respect and reverence.
