The rainbow is created with Kikkerland rainbow maker. When zooming with an iPhone the image abruptly changes at 2x zoom to a green light. What is the physics behind this?
The Rainbow Maker is a device that rotates a prismatic 'jewel' to move different colors across a space as it's struck by sunlight. Unless your experience is repeatable over a number of exposures, I'd say the thing spun so you were looking at the green portion of the spectrum instead of the blue...
I suppose you have a mobile camera with different physical lenses at the backside.
What’s happening here is that while zooming, your camera switches from one lens to another. Since the physical location of the zoom lens is different compared to the standard lens, effectively the position from which you observe the rainbow light source changes.
Now the prism that is used to create a rainbow shows a different band of light on different positions.
Apparently most of the spectrum is visible at the location of your main lens. Shifted towards the zoom lens you pickup a shifted part of the spectrum.
If you want to see the entire spectrum again with your zoom lens, shift the position of your camera to get the entire rainbow on the zoom lens.