Why do we change the sanctuary colors?

Maundy Thursday, also known as Holy Thursday, recalls Christ's Celebration of the Passover feast with his disciples on the night before he was crucified.  The Passover Feast itself, recalls the mercy of God when God passed over the homes of the Hebrew people in Egypt, sparing them from the death of every firstborn in the Land.  On Holy Thursday, Christ reimages this traditional Passover meal, replacing the sacrificial lamb with his own life, his own body and blood---which became the church's sacrament of Holy Communion.  The color in the chancel are is still purple.