[Geysers] Pearl Questions

[Pat Snyder]

Hello All!
After staring at those two pictures of Pearl, which are taken from  
the same angle (just different crops), some questions came up:

The sinter shelf color changed from white to brownish yellow, too.  
Are these signs of cooler water so cyanobacteria can grow there? Or  
is it a mineral deposit?
What are the reasons for the color change?
And is there a history of Pearl changing color like this, from blue  
to tan, and back to blue again?

Thanks for any info provided, in advance!
Pat Snyder