Jade,
The trick is that you can set variables per-row in the db_multirow, so you setup an extended column to hold the information for each row. You can do the calculation in the db_multirow code block.
Specifically for setting colors you can use CSS, of course. There are two options. You can set a "sub_class" which will append the subclass name to the class defined for the entire list, or just define the class name to use explicitly.
This way, you can define the classes semantically, just in case you decide later that the color should be different for a certain class, you can change it in the CSS file.
See template::list::element::create
