Yeah, the whole sky darkening should also be related to Rayleigh scattering, since all sunlight that gets scattered by the atmosphere will get polarized to some extent. The effect is just most intense 90 degrees from the light source.

The shimmery foil effect is likely due to birefringence. Basically some materials have a different index of refraction depending on the polarization and direction of travel, causing the light passing through to get split based on its polarization. Not sure exactly where the color shimmer comes from though tbh. I'm thinking it's some sort of interference pattern created by the polarized light components recombining out of phase or something like that, but I could be wrong about that. It's been like 4 years since I graduated with my physics degree, and optics was never my strong suit lol.

(I am taking an intro to materials science class right now though, and one of the main ways to create birefringence is passing light through a non-cubic crystal structure, so I imagine we'll probably cover that once we cover optical properties in the next few weeks. Speaking of which, martensite is the only microstructural variant of steel that I'm aware of that has a non-cubic crystal structure, so I wonder if those manhole covers you're seeing are made of martensitic steel.)