Please answer a question about the following article about IPod:

In 2006 Apple presented a special edition for iPod 5G of Irish rock band U2. Like its predecessor, this iPod has engraved the signatures of the four members of the band on its back, but this one was the first time the company changed the colour of the metal (not silver but black). This iPod was only available with 30GB of storage capacity. The special edition entitled purchasers to an exclusive video with 33 minutes of interviews and performance by U2, downloadable from the iTunes Store.

What color was the metal on the U2 version of the iPod?
black