In life, Jerry Lee Lewis, Elvis Presley, Carl Perkins, and Johnny Cash didn’t really hang out together, but they do for an entertaining 95 minutes in the musical “Million Dollar Quartet,” now playing at the Citi Emerson Colonial Theatre. Following Wednesday’s opening night, the actors who play the four legendary songwriters — John Countryman is Lewis, Tyler Hunter is Presley, James Barry is Perkins, and Scott Moreau is Cash — gathered for a festive after-party at Fleming’s Prime Steakhouse & Wine Bar.Mark Shanahan can be reached at firstname.lastname@example.org. Follow him on Twitter @MarkAShanahan. Meredith Goldstein can be reached at email@example.com. Follow her on Twitter @MeredithGoldste.