Ah. I am new to this petrol rainbow concept. Are they different from regular rainbows?Regular rainbows are formed by refraction ie splitting the spectrum, thin film rainbows occur by diffraction ie an interference pattern.
To follow up: "regular rainbows" are white light getting split into individual frequencies ("pure colors"), while "dead rainbows" are the whole spectrum minus some distinct wavelengths (depending on the thickness of the layers, one or more visible wavelengths can be removed). This means that many of the apparent colors are like magenta, cyan, and yellow, rather than red, green, and blue (at least in the first band, where only one wavelength is removed). See the Michel-LÚvy chart shown below:
michel-levy-chart.jpg (163.24 kB . 859x590 - viewed 5187 times)
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