Image of NGC 6992 shot from my house over two nights of very steady clear skies. This image still needs more signal in the red channel, but I'd need darker skies and more exposure time to get that. For more info on this object, see my earlier image here: [link]
ASA DDM60, Pentax 125 SDP, Canon 5D Mk II, IDAS LPS filter. 18 x 10 minutes at ISO 1600.
Nebulae actually work on the same principle as neon signs. If you run a strong enough electrical charge through an ionized gas, it glows at a specific color based on the ionization energy - the more energy needed, the "bluer" the color. Neon, for example, glows orange. Other colors in "neon" signs are actually other elements like argon or xenon (used because they are non-explosive and don't react if the sign is turned off). The force of the exploding star ~10,000 years ago was so strong that it is still ionizing the hydrogen (red) and oxygen (blue-green) in the Veil Nebula after such a long time.