Have you ever noticed that the color of a category and the color of the buildings it creates are the same? Just like the red Food category creates red buildings, whatever color icon you choose for your own categories will be the color used for their buildings!

For example, if you create a "Bills" category and select a green icon (see picture below), when you record an expense in this category a Lv1 tent building similar to the one used for expenses in the Housing category will appear!

Are you unsure about how to manage your own categories? Please see the "How can I set my own categories?" and "How can I sort or delete my categories?" pages for further explanation!