Can the field operative use the special ability of 3 cards and 3 disease tokens to cure purple?
How does this interact with the standard method of curing mutation of any 5 cards, with at least one having the mutation disease in the city.
From the OTB 2nd Ed. rules, page 4: "When a Scientist or Field Operative turns in fewer City cards, at least 1 of them must be a city with 1 or more purple cubes on it."
The 3 cubes turned in from the FO's card to do this must be purple (the cure color, as stated on the FO card).