Geysers and Their Pools
Just off my easel; 16" X 20" oil, 'Geyser Aqua'
The distinct color of the pools is due to bacteria and algae which inhabit the water. Different temperatures of water both cause and also permit differences in plant communities and intensities of color.
Good read, a link to Yellowstone web site on geysers; http://www.yellowstonenationalpark.com/geysers.htm