Purple during lent is symbolic of "penance", an act of devotion performed to show sorrow for a sin or other wrongdoing. During lent purple linens replace any white linens in the church and a purple scarf is draped over a wooden cross.
On Good Friday all purple linens are replaced with black to represent the death of Christ. Black linens are only used on Good Friday and Holy Saturday. The black linens are removed before sunrise on Easter Sunday.