If you get two birds, the chances are that they will bond while in quarantine and leave Saucy out, or else Saucy will only bond with one of them and inevitably one budgie ends up being the third wheel.
For this reason, I think you should get one bird. He won't mind as to the colour, maybe it's even better to get a budgie that doesn't
look like Piers as then he will move on from his sadness easier, I would think. I would say...choose whichever mutation you like as long as the chosen budgie is healthy