in office-hours session: some chunks of output text are invisible by default

Let me first say: wow, very impressive so far for the office hours workflow, including second opinion, adversarial review, state of the art checking, premise checking... This is as real as it can get. Thank you for open-sourcing it!

Now to the minor issue:
* My terminal use white background. I guess the text color is set to white sometimes.
* This mostly happens when it tries to show diff content, then some chunks are visible (black background) while others are not (due to white background).
* I have to use my mouse to select them to make them visible.