Based on historic temperature records and visual accounts, the researchers knew that Morning Glory was hotter in the past, and therefore not as inviting to the microbes that inhabit it today

The prism-pattern colors that visitors see today are primarily caused by vast communities of microbes that collect in “mats” and thrive in the pools’ hot waters, which range between 140 and 194 degrees Fahrenheit.

“It is now understood that these mats are comprised of complex communities of microbes, primarily thermophilic cyanobacteria (often called blue-green algae) and other thermophilic bacteria and archaea,” wrote lead study author Paul Nugent, a computer engineering researcher at Montana State University, and his colleagues.

Different communities of microbes lend different colors to the pool. Because the different microbes prefer different temperatures, their arrangement causes the concentric patterns of yellows, greens, browns and oranges.

The vivid blues however are the result of light scattering within the water, and signify greater depths at the center of pools like Morning Glory.

“The pool center — though presumably covered by the yellow mat — appears deep blue, indicating that the pool is deep enough that backward-scattered sunlight from the water is the dominant component of upwelling light,” wrote Nugent and his colleagues, Joseph Shaw, an optical science professor at Montana State University, and Michael Vollmer, a professor of experimental physics at Brandenburg University of Applied Sciences, in Germany.

https://808newsandinformation.wordpress.com/2014/12/21/putting-the-color-in-yellowstones-famed-thermal-springs-la-times/