Came to ask this. I suppose if the edge of the sun glows in a different color than the rest, it would tint the edge of the shadow too? So maybe appropriate for sunsets, where the sky near the sun is red but the sun itself still glows bright white. Honestly just guessing.

This seems more like a chromatic aberration "hack" for HDR landscapes (intensely-lit portions of the scene would have color fringing apparent at the boundaries of light/dark due to dispersion in the lens).

https://en.wikipedia.org/wiki/Chromatic_aberration