'blues' were originally known to intravenous drug users as azure-colored instant-release 10 mg oxymorphone, manufactured by ENDO. These were rightly considered the holy grail of pharmaceutical opiates before being discontinued due to problems with black market diversion and robberies. Many users ranked them more euphoric than heroin. They are cited in many works of fiction, notably Drugstore Cowboy.
It's so beautiful how these blues commingle with blood in the syringe.