When's the last time you laid out a site without a table element on every page?
Thursday. I was off sick yesterday.
"Oh, I want this box to highlight red when this happens!" a user might say.
Custom Events are your friend, and a sound basis for designing any complicated user-interface or series of interactions: http://developer.yahoo.com/yui/examples/event/custom-event.html So your problem above boils down to:
YAHOO.util.Event.on(thisBox, thisHappened, updateBox)
- thisBox being a DOM reference to your table cell
- thisHappened being the custom event you've defined as "this happens"
- updateBox being the function or method that probably just adds a class name to the table cell, letting the CSS apply the necessary style changes
Another good writeup of custom events is: http://nefariousdesigns.co.uk/archive/2007/07/ajaxevent-using-yui-custom-events-with-ajax/