What all can be done to the echo.

[Enkidoh]

The sepia was probably done specifically to nail down 'THIS IS THE PAST', so that nobody ever gets confused again. Probably overkill, but I don't blame them for the overcorrection, and it'd probably be more confusing to change it now, we've got a vocabulary going.

Personally though I doubt it was specificially to prevent confusion about where the Echo began and reality 'ended', as the confusion with 1.0's Echo was only really present at the beginning of the original game (during the original 1.0 starting city storyline), where the player's character was bouncing around in and out of other people's memories of ten years earlier uncontrollably and present day events were concurrently fusing with those that happened a decade before when the Archons first arrived in Eorzea. Once they joined the Path of the Twelve though and Minfilia instructed them to "use the power of the Echo", they got a handle on it and could use it "at will" (gameplay wise the game would actually prompt you to use the Echo as a choice when necessary, although this was somewhat of an illusion of choice as naturally to continue in the relevant quest you had to accept it), which meant that there was no longer any confusion about if you were in an Echo vision or not.

And as Professor Anonymoose said, even before that happened, the Echo was preceeded by a very subtle gong sound and woosh that was barely noticeable at the time, but reviewing old cutscenes of 1.0, it's amazing how obvious it is when you're actually aware of it and know what to listen for. Of course I could speculate what that gong/tolling bell really was, but I won't, given it's long been retconned out anyway and is now irrelevant.

Really, I believe that the reason why SE changed a vision through the Echo into a grainy, static-filled sepia-toned video recording was to overcome the unfortunate implications of being able to use a telepathic ability to view another's memories whenever you wish as being essentially violating that person mentally - mind rape in other words (further underlined by also retconning Minfilia in ARR into lamenting that Echo users cannot use the Echo whenever they wish, unlike her earlier instruction of the player's character in 1.0 in being able to do exactly that).

Not that I fault SE at all for feeling that way and changing it for ARR though of course (and I have to admit, the grainy old-fashioned VHS recording style of the Echo now is remarkably effective in a stylistic way if nothing else, but that just might be the 80's and 90's kid that I am talking.).