Holy Week includes all of the events leading up to, and including, Jesus death. The week starts with the Seventh Sunday in Lent, Palm Sunday. Palm Sunday marks the day when Jesus made his triumphal entry into Jerusalem. He was greeted with singing and shouting by the Jews who would later shout "crucify him!".

The next day the great crowd that had come for the Feast heard that Jesus was on his way to Jerusalem. They took palm branches and went out to meet him, shouting, "Hosanna! " "Blessed is he who comes in the name of the Lord!" "Blessed is the King of Israel!"
John 12:12-13

Maundy Thursday was the day when Jesus was betrayed. That evening he also instituted the Sacrament of Holy Communion.

The Lord Jesus, on the night he was betrayed, took bread, and when he had given thanks, he broke it and said, "This is my body, which is for you; do this in remembrance of me." In the same way, after supper he took the cup, saying, "This cup is the new covenant in my blood; do this, whenever you drink it, in remembrance of me."
1 Corinthians 11:23-25

Good Friday commemorates the day of Jesus' trial and death.

And when the centurion, who stood there in front of Jesus, heard his cry and saw how he died, he said, "Surely this man was the Son of God!"
Mark 15:39

Special Days
Palm Sunday
Maundy Thursday
Good Friday

Notes
Purple, white, and black are used in Holy Week.