Reflection nebulas scatter the light of nearby stars. Emission nebulas produce their own light due to ionization caused by hot stars embedded in their midst. Both tend to reside near the galactic plane and are confined to the permeter of the galaxy. 

But integrated flux nebulas (IFNs) are the result of extremely diffuse gas and dust at or beyond the perimeter of the galaxy reflecting the light of all the stars in the Milky Way. IFNs are very faint and are extremely hard to capture with a telescope, often requiring dozens or even hundres of hours of exposure time to unravel. 

IFNs are often accompanied by phenomena called extended red emission (ERE) and blue luminance (BL). ERE is the result of flourescence of very diffuse gas and dust. Flourescence differs from ionization in that while ionization involves the removal of an electron from an atom, floursescence involves the absorption and reimission of light from a less energetic source. BL, which is barely detectable in the visible spectrum, is similar to the process in reflection nebulas in that it is the result of light scattering. When combined, ERE and BL can combine to create a faint but deep burgundy color. Even fainter and more difficult to capture than IFNs, ERE and BL are typically accessible to amateurs only when shooting above or below the galactic plane where interference with their signal from objects inside the galaxy is at a minimum.