Background color and Font size in Categories

I need to diversify incoming mail messages.
It would be useful to allow through categories configuration about
a) Background color (not only foreground); b) Font size (for example to emphasize very important mail).

Unfortunately there is no way to change the background color, but you can change the foreground so it is the same as the category.

That way you will see all the messages in the red category in red font.

It is not possible to automatically change the font in other ways by Rule.

You can also show Smart Folders for each category, so they will appear separate from the rest. Right-click on Smart Folders and choose Categories.