Having trekked to our viewing place it was time to hang out and wait for the sun to go down and the bats of mulu to take flight.
If memory serves there were maybe four of us tourists and a couple of guides. As we were waiting a band of showers crossed the mulu hills. In fact, best I can tell, I never got a clean shot of Mount mulu. Every shot I have shows the mountains shrouded in cloud.
In the photo below, a light shower drifts across the other side of the valley while the sun, dipping to the west but still quite high in the sky, reflects off the falling raindrops as a rainbow. The rainbow is formed when sunlight enters the water droplet and is refracted, then gets reflected off the back of the water droplet and refracted again on exiting the droplet. The point of maximum intensity occurs at an angle between 40 and 42 degrees to the line between the observers head and its shadow. So the higher the sun is in the sky, the closer the rainbow's arc is to the horizon. When the sun climbs above 42 degrees, the rainbow is below the horizon, so you can't see it unless you're in a plane or on a mountain. This is why the strongest and most impressive rainbows occur shortly after sunrise or just before sunset where the top of the arc approaches it's maximum 42 degrees of elevation above the horizon.
The separation of colors is a human eye thing. If this photo were in black and white there's just be a peak in the intensity where the rainbow is but no actual separation of luminosity or brightness to show the color banding.
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