user: Mark puts his blue basketball in a wooden box and closes it. Mark doesn't know it, but this is a magical box, which changes colors of things that are left inside. After a few minutes, the basketball turns green, but then turns blue again. Mark looks at the box but cannot see what is happening inside. Mary calls Mark and asks him what is the color of his ball. Mark tells her the truth. What does Mark tell Mary?

assistant: Before opening the box, Mark calls his friend to tell them that the color of the basketball is blue.