Really nice game, well done!
Here are some things you could improve:
- Highlight the selected tab. At first, I thought I were in the diplomacy tab because it is another shade of grey.
- Display the nobles' current mood somewhere, perhaps in the "News" screen? For me, loss came somewhat unexpected while I was focusing on getting my food and population gradient into the positive.
- Perhaps make the start of the game more intuitive − several buttons just tell you that you have to have some other resource; you could perhaps grey them out.