KT at io9 explains:

Only a small portion of the Veil Nebula — located in the constellation Cygnus — is only partly visible to the Hubble Telescope. But what can be photographed is fairly impressive.

This is the "south-eastern knot" of the Veil Nebula, which is 50 lightyears across and 1,500 lightyears away from Earth. Formed as it is by a supernova, the colors come from heated gas as the outer layers of a star's detonation meet with the rest of space. In this image — originally taken in July, 2007 — blue is oxygen, green is sulphur, and red is hydrogen.

It's a beautiful image of a nebula, which looks like a piece of silk waving in air.

Source: http://io9.com/impossibly-the-veil-nebul...