The colors you see in this photo are bacteria. The center of the spring which is blue is too hot to support life, but in the slightly cooler water on the edges of the pool bacteria lives. The Bacteria range in colors from green to red depending on the temeratures at which they live.
Grand Prismatic Spring - Yellowstone National Park, Wyoming
You are officially one of my new photography heroes! I've been to this pool and it's really quite a sight, although I was having a hard time capturing it on camera and really giving it justice. You did a great job! And again, truly fantastic gallery!
Skill and better cameras win everytime!
Great photo, and definitely worth the walk.