Nebulae are huge expanse of gas, much more rarefied than the air we breathe. This gas is made of almost 90% of hydrogen, the most abundant element of the Universe. Many nebulae show the typical red hue. It's nor a coincidence or an effect of image post-processing: the red hue is due to hydrogen heated up to 10000 °C by the UV light of the stars.


If you love technical data, take a look at my Astrobin gallery and you will find anything you need.