The Amur System is a small, several planet system to the Galactic North-East, straddling the border between the Mid Rim and the Outer Rim. The Amur System, during the times of the Galactic Republic, was a massive hub of commerce, as within it laid a large Gas Giant of Tibanna Gas. As it's primary source of income, the Amurian System government, untrusting of the Jedi's promises of peace, as well as their mere existence, siphoned funds from the sale of it's gas, and formed a private Defense Force for the System, combining Plastoid VAC-Sealed armor, Exo-Suit Augmentations, Genetic Manipulation, Tibanna-Based Blaster weaponry, 'Smart' weapons, high quality Slugthrowers, and both conventional and unconventional Ballistic Missile ordinances into a deadly, and surprisingly efficient military.
As time went on, the Amurian System's System Defense force evolved into a proper System Military becoming more and more openly funded by the various planets in the Amur system, and conversely, it's military traditions began to seep back into the populace of the System, and while this tradition began to worry certain neighboring systems, come 22 BBY, however, Amur's constant preparations came to a heed as the Clone Wars broke out. During the three years of the Clone Wars, the Amurian military provided one of the best instances of System Defense, despite straddling the border of Republic and Separatist space, excelling in any and all combat brought their way, even so much as sending detachments of elite troops to join the Galactic Republic in battling out of System, earning those soldiers their Green Decals and Trim.
At the end of the Clone Wars, as the Galactic Republic was reformed into the Galactic Empire, the system split into a bloody civil war, as those that supported the Galactic Empire drove out Republic loyalists and idealists alike, continuing to do so up until fall of the Galactic Empire. Many of these Loyalists would later join the Rebellion or look for Mercenary work, doing everything in their power to damage the Galactic Empire in any way possible.
Those troopers that were driven out painted themselves with the Green Decals and Trim of veterans, both to insult the Government that they felt betrayed them, and as a promise to continue the fight until they are one day welcomed home as heroes.