Surely your J'ochre - ing!
Yellow in color and dizzying to look down.
Actually, I thought the same thing when I was there. One spends so much time at the geysers and bubbling mudpots that when one gets to the canyon, it IS a surprise to see yellow stone. The whole place it a shock to the senses.
I would only have been surprised to see yellow stone if it had been named, say, Purplestone Canyon. (Don't think it would be nearly as famous, though.)
What do you think?