I just watched Kingdom of Heaven (Again), which I know is a piece of fiction in as much as a lot of the names and details are slightly different. I know, however, that the majority of the general facts were true; that Guy de Lousingon charged out to meet Saladin's Army, and was defeated at Hattin, and that Bailin of Ibelin commanded the defence of Jerusalem, and eventually handed over the keys to Saladin, whom let many of the civilians leave peacefully to avoid another massacre like in 1099.
So, my question pertains to the individual factions of the Christian Army. We see, in a lot of these films, the Knights Templar, those in white tabards bearing a red cross, but who were they? Who were the Knights Hospitalier, in the black tabards with white cross? And what of the blue cloaks and gold crest? Were there any others, and what were their roles?
To call details slightly different is a massive, incredible understatement. Perhaps the only thing that Kingdom of Heaven got right is that people do inhabit a place on Earth called Jerusalem.
To give the simplest answer there were many factions within factions. The Knights Templar, also known as the Poor Fellow-Soldiers of Christ and of the Temple of Solomon, exerted varying degrees of power and influence, and in and among themselves saw various quarrels about what constituted appropriate actions or reactions to Saracen incursions and vice versa. A large part of Guy de Lousingon's character in Kingdom of Heaven was heavily modeled after Gerard de Ridefort, the Grand Master of the Knights Templar until 1189.
Ridefort routinely feuded with Raymond of Tripoli and his Ibelin faction.
They quarreled over a succession crisis from King Baldwin.
They quarreled over the other crusader kingdoms.
They quarreled over Hattin.
There was lots of feuding and political in fighting and intrigue, but the hyper majority of it was far more nuanced and interesting.
An interesting, though controversial source (since it is adamant on Richard I's homosexuality) is Warriors of God by James Reston Jr.