Elliptical NGC 205 Lenticular Irregular Large Magellenic Cloud Classification of Nebulae Nebulae are large clouds of gas. Reflection nebulae reflect the light from nearby stars. Planetary nebulae are created when a light red giant throws off it's outer layers. They come in a variety of colors. Our sun will create a planetary nebula in billions of years.
Dark nebulae are just that - dark.
The gas that makes them up is dense and does not allow light to pass through. We see these because they block light from behind them. Supernova remnants are left over after a supernova explosion of a star. If we were to watch these over tens of thousands of years, we would see these clouds slowly drift apart, starting out like a cloud of gas and expanding to become thin strings of gas. These, too, come in many colors.