The GC Rules (ACA Nov 2013) state:
5(a) The side which wins the toss plays first with the blue ball or the equivalent alternative colour.
5(f) ….If it is noticed that a wrong ball has been played before all four balls have been played into the game, Rule 11 does not apply and the game reverts to its state after the last turn played correctly in sequence.
Since Yellow has been played in, then all four balls have been played in, and 5(f) does not apply - the playing of Yellow condoned the previous wrong ball plays. Blue should now play….
It does not matter whether it is Singles or Doubles.
0412 178 254