I've saw this image on a Facebook page, it is in portuguese, but there is the explanation; the Pokémon images on the official site all have a different background color. Sylveon and Fletching have different colors; and the colors seems to be related to their types. This means that Sylveon is not a Flying-type since Fletching's background color is blue and Sylveon's background color is pink.
Oh, and as of note, Sylveon cannot be a Psychic-type because the supposed new Mewtwo form has a different background color (purple). This is an heavy evidence that there will be a new type.
The image in question is: