It's interesting to compare Bluray and DVD releases, because the makers in most cases end up differentiating between the two in the colour representation of the cover images. Sort of like how they try to show advertisements for high-definition TVs on regular TVs, trying to illustrate the difference in image quality by simply using a clip with boosted contrast and saturation for the "high-def" experience.
In the case of Black swan though, it's not only colours that's undergone a change...
First the DVD and Bluray covers.
But something looks a bit off, let's outline the edge of Ms. Portman (brightened a bit to see the real outline hidden in the shadows).
And now the same outline applied to the Bluray cover.
It appears as if the makers of the Bluray also felt the need to show the splendidness of the format by slimming down the face of the lead actress. Buy Bluray for even slimmer ladies!