The yellow kit is inspired by Southampton's 1976 FA Cup final victory over Manchester United. FA rules state that from the semi-final stage onwards, clubs must wear a kit registered at the start of the season, but an exception has been made. The club said in a statement: "The club is pleased to have been granted permission to wear the commemorative '76-inspired yellow kit that has been a permanent fixture of this season's FA Cup run for the victories over Doncaster, Leicester, Fulham and Arsenal."
Southampton beat Arsenal 2-1 in the quarter-finals, with goals from Ross Stewart and Shea Charles. The winner of the semi-final will play either Chelsea or Leeds in the final on May 16.
In the league, Southampton beat Wrexham 5-1 on Tuesday to move into play-off spots. They have a game in hand on all but one of the teams in the play-off mix. Tonda Eckert was appointed Southampton manager in December after a successful interim spell. Speaking after the Wrexham win, Eckert said: "I think we are at a good moment physically and mentally, but we will need to close this game tonight, recover tomorrow and go again."