The doctor says: "Oh my god, your leg is infected. We need to amputate your leg, otherwise the infection will spread in your entire body and will kill you."
So the doctor amputates the left leg of the man and gives him crutches.
A week later, the man goes to the doctor again and says: "Doctor, my right leg has now turned blue."
The doctor says: "Oh no! I guess the infection spread to your right leg. We need to amputate it too, otherwise the infection will spread to the rest of your body."
So the doctor amputates the right leg of the man and gives him prosthetic legs.
A week later, the man goes again to the doctor and says: "Doctor, the prosthetic legs you gave me have turned blue. How is that even possible?"
The doctor says: "Now I understand your problem. You jeans is giving out its color."