As some wiccan group requires nudity during rituals, because some think clothed body does not radiate energy as naked, others prefer wear robes during rituals and magic.
Reasonal use for using robe/cloak is that when you use just certain clother when performing magic, it helps creating correct atmosphere, and in the later helps transferring your thoughts to proceeding ritual thus enchaning your ritual consciousness.
Colors are used because of their vibration. Black robes are very popular because it symbolizes night, university and clearity and is very protective. When wiccans wears black robe, he or she respect blackness of outerspace which represents source of divine powers.
Here are few color options: Yellow for fortune-tellers, blue for healers. Green gives energy when working with herbs and brown for those who do spells with animals. Purple robes are weared by those who work with pure, divine power and white who wish to symbolize cleaning and spiritual cleaness. White is also good for meditation and cleaning rituals. White is used in the festives of the full moon.
Orange and red robes are used in sabbaths, in rituals for protection and “tuning-in” into divine energies in his solar form.
Blessing of the Robe