User blog comment:Squedswag/E.N.D. Theory: Possibly that Nasu will stay alive even if he kills Zeref/@comment-30178157-20170105013017/@comment-7418318-20170105201201

Natsu didn't use purple flames even then.

He used his regular red/orange/yellow flames, but changed the properties in the way Macao told him.

So no, Natsu can't use purple flare or any other kind of purple fire. He can eat it if someone else shoots it at thim, but that's all.

The only possible exception was that stuff he ate from the Eclipse Leo (I don't remember the colour and don't want to watch that crappy filler arc to check), but that was just something he had temporarily like God Flames.