The water comes from deep within the earth, and picks up minerals from the crust as it travels. Black smokers are the hottest, with temperatures ranging from 300 to 400 degrees Celsius. At this temperature there are high levels of sulfide and metals dissolved in the hydrothermal fluid. The fluid in white smokers is cooler, ranging from 100 to 300 degrees Celsius. At this temperature, the fluid does not contain the minerals that make it black.
Some plumes have no color and appear to shimmer.