Investigated on a 5.1dev version, initially found on a 4.4.6 version.

Adding a new comment on the "Submissions" page of an Assignment creates a comment box that has no sufficient contrast.

By removing the text color and modifying the background color of a newly added comment to #fcefdc (the same color as --bs-warning-bg-subtle), it could pass (at least) the WCAG AA requirements for the links and the text.

The same problem occurs on the assignment page when a comment is added.

Looking in the tracker I seem to understand that some work needs to be done on the Comment UI (like ditching YUI and converting it to ESM), but this bug could be easily fixed in the meantime.

Steps to reproduce :

1. Create a course with at least one student S1 enrolled.
2. Create an Assignment in the course.
3. Grade the student S1 (if not you cannot add any comment)
4. Go to the "Submissions" page of the assignment.
5. Open the "Comments" menu in the row of any student.
6. Add a new comment.
7. Check the contrast for the new added comment (yellow background)