Your answer, "scarlet", is not correct.
The correct answer to
What color was Jesus' robe when he was crucified?
is
purple
as shown by
Mark 15:17
which is
- KJV
- And they clothed him with purple, and platted a crown of thorns, and put it about his head,
- NIV
- They put a purple robe on him, then twisted together a crown of thorns and set it on him.