The Tampa Bay Rays were established in 1998 but at the end of June the team will debut "faux back" uniforms from 1979, according to Chris Creamer of Sportslogos.net:
The Tampa Bay Rays are planning on holding a Turn Back the Clock game where they will wear the uniforms of the 1979 Tampa Bay Rays. [T]he logo and jersey script is not the same as the current 2012 Rays looks, it’s all been re-created to look as if it was designed in the ’70s.
According to the report, the turn-back-the-clock game will be held on June 30 against the Detroit Tigers. The 1970's band, "Earth, Wind and Fire," will perform after the game.
Pictures of the vintage uniforms haven't been released yet, but as Creamer describes, the uniforms will likely include:
the cap with the alternate coloured front-panel, the pullover jersey with sleeves in another colour from the base, thick sleeve striping and some good old-fashioned powder-blue.