The "home" team for the Super Bowl will be the Cardinals, thanks to the alternating scenario -- the NFC is "home" after even-number years and the AFC after odd-numbered years (and this is still the 2008 season).
That means the Cards will be wearing their red jerseys and the Steelers will be wearing white. For those who might be confused counting back seasons -- and the Steelers wearing white in their Super Bowl win over the Seahawks after the 2005 season, yes, Pittsburgh was "home" that year. But the Steelers had come through the playoffs with three road victories, and they didn't want to mess with their mojo. So they stayed with their road unis.