This potion affects the mind of the character so that he or she believes the liquid is some other potion (healing, for example, is a good choice - damage is “restored” by drinking it, and only death or rest after an adventure will reveal that the potion only caused the imbiber to believe that he or she was aided). 

If several individuals taste this potion, it is still 90% probable that they will all agree it is the same potion (or whatever type the DM announces or hints at).