Purple, often a somber, dark shade, is worn during the penitential seasons of Advent and Lent. Purple signifies great solemnity, with connotations of both penance and royal dignity.
Purple is associated with mourning and so seeing it helps us anticipate the memory of the pain and suffering of the crucifixion. Purple is also the colour associated with royalty because it was originally a color only the wealthiest could obtain.Jesus was clothed in purple as a sign of royalty, but also in mockery of His claim to be the promised Messiah and heir to the throne of David.
As Christians we prepare for our King through reflection and repentance, therefore purple is the perfect penitential color.