White greca

Now these coats, even for Cardinals, are usually worn in black. But knowing Gammarelli's, I expect if you walked in there and said "Look, I'm Pope John the twenty-fourth and I need a white Greca", they would probably ask if you wanted it in polycotton, wool or mohair.
Update: White greca experts have posted links to pictures of several other Popes sporting this garment - see the combox.