This is simply the fluff for my Blood Angel successor chapter, the Azure Prophets.

Originally founded as the Crimson Dragoons, the Azure Prophets took thier title on the world of Vernal VI while they campaigned agaisnt foul heretics seeking to spread the word of their foul god Khorne.
The initial stages of the campaign were marvelously successful and it looked as though the chaos insurrection would be defeated in under a year. Arbites and PDF forces had prevented the cult from spreading to cult areas while the Astartes lauched successful seek and destroy missions. It wasn't until the Crimson Dragoons faught their way into the final enemy stronghold and the chapters chief librarian entered combat with the arch-heretic, a foul chaos lord of the World Eaters legion.
The Khorne Lord had, surprisingly, thought ahead and held all his chaos marine forces until he could meet the loyalist Astartes in whole. While fighting overtook the great complex, the most critical fight was between Tyrus, chief librarian of the Crimson Dragoons, and the Khorne Lord, whose name was never recorded. Despite his formidable psykic abilities Tyrus found himself outmatch by the warrior of the blood god and took a desperate gambit in hope of victory: he gave into the Black Rage completely.
As he felt his concious go, supplanted by visions of Sanguinus' last moments, the fight turned in his direction. The Rage gave him the speed and strength neccessary to overpower his opponent. A quick thrust of his force halberd cleaved the Khornites head from his neck and, without the manifestation of Khorne to lead them, the Chapters forces began to overpower the World Eaters.
It was only after the fight that the chapter saw their librarian that had sacrificed so much for them. He was a broken marine, the visions of Sanguinus' death having worked through his mind, driving him insane. He was locked up in the chapter's fortress monestary.
As his visions drove him closer to complete destruction he didn't even recognize when a stillness came over his mind. A new vision took over, a vision of Fortress Terra under attack. He knew instantly that this wasn't the Heresy as marines of his chapter fought besides marines of the Space Wolves, neither of which had been at the Siege of Terra. The time period didn't matter though, the lose seemed just as certain.
The loyalist forces were slowly driven back to the inner palace when suddenly an azure light lite the sky. Out of it came Sanguinus, clad in the brightest regal blue, and behind him came the primarchs, all of them found and brought back for the end. With them at their side the loyalist fought like warrior gods.
Longing to see the end to this glorious fight Tyrus advanced with his fellows until Sanguinus himself stopped him. Tooking him dead in the eye, the glorious angel declared, "This isn't for your eyes. Get up and serve your chapter."
Awakening, Tyrus no longer felt the bite of the Rage. He seemed to have surpassed it. Though his guards questioned his sanity they did eventually let him go. Eventually, knowledge of his visions spread to the whole chapter. The Sanguary Priests and Chaplians questioned him for days. Eventually, it was decided that Lord Sanguinus had spoken to the chapter through his servant Tyrus. The awe at this monumentous moment spread to such a fevered pitch that the chapter master declared that their name would reflect the message.
They would be known as the Azure Prophets. Their armor, in emulation of Sanguinus, would be the brightest blue. In difference to their past though, the left hand and right leg (two places Tyrus had been wounded by the Khorne Lord) would still be painted red. Their mission was to maintian the Imperium until Sanguinus' return, at the head of the Primarchs, at the end.