It makes me sad to realize that there is some deep-seated part of the human psyche that cannot see something beautiful without wanting to fuck it up.

So basically it's garbage that's changing the color?

Most famously, the Morning Glory Pool used to be bright blue; it’s now more commonly known as “Fading Glory” or, even more accurately, “Garbage Dump,” because of what happened when humans started clogging it with trash. And for the first time, researchers have come up with a model to explain why.

Writing in the journal Applied Optics, researchers at Montana State University and Brandenburg University of Applied Sciences in Germany determined that the unique characteristics of Morning Glory Pool, along with Sapphire Pool and the Grand Prismatic Spring, are related to the springs’ temperatures. Back before Yellowstone became a National Park in 1872, they explain, Morning Glory was significantly hotter, and bluer. But over the years, an “accumulation of coins, trash and rocks” began to block the underwater vent heating the pool, causing its temperature to drop. That, in turn, created a change in the spring’s microbial mat — the complex community of microbes dependent on its hot waters — ultimately shifting the appearance of the shallow waters to the orange, yellow and green spectrum we see now.

List of things people dropped into the geyser:

http://www.yellowstonepark.com/2014/03/this-is-yellowstone-things-stuffed-down-a-geyser/