Why does Sirius A blink in many colors?

[sophiecentaur]

Googling caustics gives me images like this:
https://en.wikipedia.org/wiki/Caustic_(optics)#/media/File:Kaustik.jpg
but nothing about color changes

The shape of the caustic curve depends on wavelength. The light from Sirius contains wavelengths right across the visual range so the caustic effect is working on a bigger range of wavelengths (a whole octave). Where the equivalent effect on a cooler star will be mostly on the Rs and Gs - producing a range of reds and yellows, mainly, the effect on the light from Sirius can be to eliminate the Rs and just leave the Gs and Bs - not a usual thing to see and remarkable to the eye. But remember our very idiosyncratic perception of colour. It's hard to predict or explain accurately our subjective appreciation of such a relatively rare object under unusual (dark) conditions. A camera with high IR sensitivity could perhaps 'see' more significant 'colour' changes for a cool star.

 

[andrew s 1905]

There has to be enough refraction and chromatic aberration such that the different colored images are so separated from each other that they sample independent optical paths,

Yes I agree I was assuming in points 1 and 2 and should have made it explicit. Andrew