What is the meaning of the different colored drapes on the cross?

The cross is draped in black on Good Friday, representing the death of Christ  on the cross for our sins.

The cross is draped in white on Easter Sunday, representing the resurrection of Christ and that He was "...raised again for our justification."

The cross is draped in purple (the color of royalty) on Palm Sunday, the day Christ entered Jerusalem as King riding a donkey. Jesus is indeed the King of the Jews, but much more, the King of kings and Lord of lords.

Where the good news of Jesus Christ is proclaimed in truth and love.