I'm wondering why the resources on the City boards have colored backgrounds? It is quite confusing when you play cards such as Vineyard, Bazaar or Chamber of Commerce since the starting resources do not count in those cases. Is there any reason for it besides it can be considered more aesthetic this way?
From the rulebook:
The resources a player can buy from their neighboring cities are:
• the resources initially produced by the city (as indicated on the board)
• the resources from its brown cards (raw materials)
• the resources from its gray cards (manufactured goods)
However, it is impossible to buy the resources produced by some commercial structures (yellow cards) or by some Wonders: these resources are reserved to their owner.
Since resources initially produced by cities behave identically to resources produced by brown/gray cards, it is good enough reason to color them same way, to distinquish them from non-buyable resources.
I can’t think of a gameplay-related reason, i.e., there is no game function that would make use of the top-left color on the wonder boards.
Using the color associated with the effect (brown for raw materials, grey for manufactures goods, yellow for commerce stuff, white for leader stuff) seems to make sense. It can help in various cases, e.g., when scanning the boards of your neighbours, you immediately see the effect’s category and if it’s relevant to your need.
I don’t think it’s confusing. The effects on cards like Bazar, Vineyard, and Chamber of Commerce show colored cards, not colors. In my experience (after several hundreds of games) new players grasp this quickly: don’t count in the brown/grey wonder effect when you have to count brown/grey cards.