Dragons are incredibly greedy creatures, having a strong desire to possess anything shiny, valuable-looking, or truly valuable. This holds true for both benevolent and malevolent dragons.
Muria noticed it in himself due to his Golden Dragon lineage. He had developed a penchant for collecting all sorts of precious treasures, had constantly instructed the Tidal Giant who had pledged allegiance to him to search for treasures in the sea, and had never entertained the idea of ordering the giant to stop his search.
Muria realized the influence that this bloodline had on him but made no conscious effort to correct it, considering there were no adverse effects. Besides, his lust for treasures was not as intense as that of a True Dragon.
Driven by dragon greed, Muria devised a rather unscrupulous plan. For the Five Colored Dragons, he established magic arrays, instigated disciplinary measures, and correspondingly, he also established a reward system.