As the 'home team' for the Super Bowl the Bengals get to pick their uniform first and will undoubtedly pick one of their usual home jerseys - either black or orange.
The Rams designated their blue and bone jerseys as their 'standard' jerseys and the modern throwback (white) jerseys as their alternates. Which means they can't wear their modern throwbacks in the Super Bowl.
From this site: [
www.nfl.com]
Los Angeles introduced its alternate top, which it termed the "modern throwback,"... and teams can't wear their alternate jerseys in the Super Bowl. So bone it is.
From this site: [
en.wikipedia.org]
Teams are only permitted to wear alternative jerseys once in playoff games (except the Super Bowl, where teams must wear their standard uniforms)
AlbaNY_Ram