Is a Freudian index, if you are unintentionally telling the truth or if you are unintentionally says something that is not true?
not completely. An example so it becomes clearer:
in a text about the theater is: "dramendreick". And you read: "Steam triangle".
Then your imagination played a prank. Freud would have cheered.
If you pronounce that what you just think, but it does not want to pronounce.
That does not necessarily have to be the "truth", just about your intention, what you wanted to say.
If anyone's question: "What color does the grass have?"
Then you think: Mh, it's natural but would be funny if it was blue.
You answer truthfully: "The grass is blue" -> Freudscher encourder, you wanted to say truthfully "green".