It does not appear to be a syntax or linting warning, nor does it resemble any typical highlight associated with code cells or markdown.

For me, it does, the sections written in color show there is a code cell with a warning or an error (I also use Pylance).

For example, here I don't have error or warning :

With a warning, I have an orange text and an orange circle :

With an error, I have a red text and a red circle :

(note: here i'm not using any version control system like git)