Basically two common types of fluid. Petroleum based (MIL-H-5606) which is red in colour (dyed for identification) Explosive in a mist, which is how a lot of hyd leaks manifest themselves. So, in the fifties, Phosphate Ester (Skydrol) was introduced for commercial aircraft. The military don't seem bothered by possible explosions.....
so Skydrol's not commonly used by them.
One of the best sources of info on hydraulics in general is the US Navy - they have some very clear and concise manuals.
This is quite useful;
http://www.tpub.com/content/aviation.../14018_178.htm