What color is Botox supposed to be in the syringe?

Botox is clear when when reconstituted properly.  Might the injector have been using a yellow syringe (I have not seen one but I suppose one could exist).

Botox is reconstituted (mixed) with saline in the office and should always be a clear liquid. There is no reason it should ever be a yellow color. I would be very concerned that the product was not Botox or it was mixed incorrectly. I recommend having your treatments performed by a board certified dermatologist or plastic surgeon.