Voters in the western state of Colorado will decide next month if they want their state to have a single-payer health care system. Under such a system, private health insurance companies would no longer operate in the state. The government would pay all health care costs from a new tax. In some countries, health care workers are government employees. Under the Colorado plan, doctors would still work for themselves or for hospitals or clinics. But the government not their patients or private health insurance companies would pay them. That money would come largely from a new 10 percent income tax. Most older Americans currently get health care from a government-paid system called Medicare. And many poor people in the U.S. get health care from a government-paid system called Medicaid. However, those who oppose Colorado’s plan say they do not want the government to become involved in their health care.